Cannot wrap around in popup_filter_menu()

Currently, it is not possible, to wrap around at the end of the list
using e.g. down (and go back to the top) or up at the beginning of the
list and go directly to the last item. So let's just allow this.

fixes vim#12689

Adjut test

src/popupwin.c

@@ -2560,12 +2560,20 @@ f_popup_filter_menu(typval_T *argvars, typval_T *rettv)
     res.v_type = VAR_NUMBER;
 
     old_lnum = wp->w_cursor.lnum;
-    if ((c == 'k' || c == 'K' || c == K_UP || c == Ctrl_P)
-						      && wp->w_cursor.lnum > 1)
-	--wp->w_cursor.lnum;
-    if ((c == 'j' || c == 'J' || c == K_DOWN || c == Ctrl_N)
-		       && wp->w_cursor.lnum < wp->w_buffer->b_ml.ml_line_count)
-	++wp->w_cursor.lnum;
+    if (c == 'k' || c == 'K' || c == K_UP || c == Ctrl_P)
+    {
+	if (wp->w_cursor.lnum > 1)
+	    --wp->w_cursor.lnum;
+	else
+	    wp->w_cursor.lnum = wp->w_buffer->b_ml.ml_line_count;
+    }
+    if (c == 'j' || c == 'J' || c == K_DOWN || c == Ctrl_N)
+    {
+	if (wp->w_cursor.lnum < wp->w_buffer->b_ml.ml_line_count)
+	    ++wp->w_cursor.lnum;
+	else
+	    wp->w_cursor.lnum = 1;
+    }
     if (old_lnum != wp->w_cursor.lnum)
     {
 	// caller will call popup_highlight_curline()

src/testdir/dumps/Test_popupwin_menu_scroll_3.dump

@@ -1,9 +1,9 @@
 >1+0&#ffffff0| @73
 |2| @73
 |3| @29|╔+0#0000001#ffd7ff255|═@10|╗| +0#0000000#ffffff0@30
-|4| @29|║+0#0000001#ffd7ff255| |s|e|v|e|n| @3| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
-|5| @29|║+0#0000001#ffd7ff255| |e|i|g|h|t| @3| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
-|6| @29|║+0#0000001#ffd7ff255| |n+0&#e0e0e08|i|n|e| @3| +0&#ffd7ff255| +0#0000000#0000001|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
+|4| @29|║+0#0000001#ffd7ff255| |f|i|v|e| @4| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
+|5| @29|║+0#0000001#ffd7ff255| |s|i|x| @5| +0#0000000#0000001|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
+|6| @29|║+0#0000001#ffd7ff255| |s+0&#e0e0e08|e|v|e|n| @2| +0&#ffd7ff255| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
 |7| @29|╚+0#0000001#ffd7ff255|═@10|╝| +0#0000000#ffffff0@30
 |8| @73
 |9| @73

src/testdir/dumps/Test_popupwin_menu_scroll_3a.dump

@@ -0,0 +1,10 @@
+>1+0&#ffffff0| @73
+|2| @73
+|3| @29|╔+0#0000001#ffd7ff255|═@10|╗| +0#0000000#ffffff0@30
+|4| @29|║+0#0000001#ffd7ff255| |s|e|v|e|n| @3| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
+|5| @29|║+0#0000001#ffd7ff255| |e|i|g|h|t| @3| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
+|6| @29|║+0#0000001#ffd7ff255| |n+0&#e0e0e08|i|n|e| @3| +0&#ffd7ff255| +0#0000000#0000001|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
+|7| @29|╚+0#0000001#ffd7ff255|═@10|╝| +0#0000000#ffffff0@30
+|8| @73
+|9| @73
+@57|1|,|1| @10|T|o|p| 

src/testdir/dumps/Test_popupwin_menu_scroll_6.dump

@@ -1,9 +1,9 @@
 >1+0&#ffffff0| @73
 |2| @73
 |3| @29|╔+0#0000001#ffd7ff255|═@10|╗| +0#0000000#ffffff0@30
-|4| @29|║+0#0000001#ffd7ff255| |o+0&#e0e0e08|n|e| @4| +0&#ffd7ff255| +0#0000000#0000001|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
-|5| @29|║+0#0000001#ffd7ff255| |t|w|o| @5| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
-|6| @29|║+0#0000001#ffd7ff255| |t|h|r|e@1| @3| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
+|4| @29|║+0#0000001#ffd7ff255| |f+0&#e0e0e08|o|u|r| @3| +0&#ffd7ff255| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
+|5| @29|║+0#0000001#ffd7ff255| |f|i|v|e| @4| +0#0000000#0000001|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
+|6| @29|║+0#0000001#ffd7ff255| |s|i|x| @5| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
 |7| @29|╚+0#0000001#ffd7ff255|═@10|╝| +0#0000000#ffffff0@30
 |8| @73
 |9| @73

src/testdir/dumps/Test_popupwin_menu_scroll_6a.dump

@@ -0,0 +1,10 @@
+>1+0&#ffffff0| @73
+|2| @73
+|3| @29|╔+0#0000001#ffd7ff255|═@10|╗| +0#0000000#ffffff0@30
+|4| @29|║+0#0000001#ffd7ff255| |o+0&#e0e0e08|n|e| @4| +0&#ffd7ff255| +0#0000000#0000001|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
+|5| @29|║+0#0000001#ffd7ff255| |t|w|o| @5| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
+|6| @29|║+0#0000001#ffd7ff255| |t|h|r|e@1| @3| +0#0000000#a8a8a8255|║+0#0000001#ffd7ff255| +0#0000000#ffffff0@30
+|7| @29|╚+0#0000001#ffd7ff255|═@10|╝| +0#0000000#ffffff0@30
+|8| @73
+|9| @73
+@57|1|,|1| @10|T|o|p| 

src/testdir/test_popupwin.vim

@@ -1794,7 +1794,8 @@ func Test_popup_menu()
   let winid = ShowMenu(" ", 1)
   let winid = ShowMenu("j \<CR>", 2)
   let winid = ShowMenu("JjK \<CR>", 2)
-  let winid = ShowMenu("jjjjjj ", 3)
+  " wraps around
+  let winid = ShowMenu("jjjjjj ", 1)
   let winid = ShowMenu("kkk ", 1)
   let winid = ShowMenu("x", -1)
   let winid = ShowMenu("X", -1)
@@ -3053,20 +3054,28 @@ func Test_popup_menu_with_scrollbar()
   call term_sendkeys(buf, "jjj")
   call VerifyScreenDump(buf, 'Test_popupwin_menu_scroll_2', {})
 
-  " if the cursor is the bottom line, it stays at the bottom line.
+  " the cursor wraps around at the bottom
   call term_sendkeys(buf, repeat("j", 20))
   call VerifyScreenDump(buf, 'Test_popupwin_menu_scroll_3', {})
 
+  " if the cursor is again at the bottom line
+  call term_sendkeys(buf, repeat("j", 2))
+  call VerifyScreenDump(buf, 'Test_popupwin_menu_scroll_3a', {})
+
   call term_sendkeys(buf, "kk")
   call VerifyScreenDump(buf, 'Test_popupwin_menu_scroll_4', {})
 
   call term_sendkeys(buf, "k")
   call VerifyScreenDump(buf, 'Test_popupwin_menu_scroll_5', {})
 
-  " if the cursor is in the top line, it stays in the top line.
+  " the cursor wraps around at the top
   call term_sendkeys(buf, repeat("k", 20))
   call VerifyScreenDump(buf, 'Test_popupwin_menu_scroll_6', {})
 
+  " the cursor at the top of the window again
+  call term_sendkeys(buf, repeat("k", 3))
+  call VerifyScreenDump(buf, 'Test_popupwin_menu_scroll_6a', {})
+
   " close the menu popupwin.
   call term_sendkeys(buf, " ")