Strip whitespace in latexsub :exit-function

According to the docstring for completion-extra-properties, the "STRING" passed to the
:exit-function should be the bare text to which the field was completed, but helm-mode adds
an extra space at the end of "STRING". Since none of our latexsubs include whitespace, we
can safely strip whitespace in the :exit-function and work around this helm bug.

I will file an upstring bug report against helm, but I think it's worth fixing quickly here
since it's only a simple 3-line change.

Closes #204.

julia-mode-tests.el

@@ -963,6 +963,8 @@ end" 'end-of-defun "n == 0" "return fact(x)[ \n]+end" 'end 2))
   (should (equal (julia--call-latexsub-exit-function
                   "\\kappa\\alpha(" 7 13 "\\alpha" t)
                  "\\kappaα("))
+  ;; Test that whitespace is stripped from `:exit-function' NAME for compatibility with helm
+  (should (equal (julia--call-latexsub-exit-function "x\\alpha " 2 8 "\\alpha " t)  "xα "))
   ;; test that LaTeX not expanded when `julia-automatic-latexsub' is nil
   (should (equal (julia--call-latexsub-exit-function "\\alpha" 1 7 "\\alpha" nil) "\\alpha"))
   (should (equal (julia--call-latexsub-exit-function "x\\alpha " 2 8 "\\alpha" nil)  "x\\alpha "))

julia-mode.el

@@ -910,8 +910,12 @@ buffer where the LaTeX symbol starts."
         ;; <https://github.com/abo-abo/swiper/issues/2345>). Instead of automatic
         ;; expansion, user can either enable `abbrev-mode' or call `expand-abbrev'.
         (when-let (((eq status 'finished))
-                   (symb (abbrev-symbol name julia-latexsub-abbrev-table))
-                   (end (+ beg (length name))))
+                   ;; helm-mode passes NAME with an extra whitespace at the end. Since
+                   ;; `julia--latexsub-start-symbol' won't include whitespace, we can safely
+                   ;; strip whitespace.
+                   (clean-name (string-clean-whitespace name))
+                   (symb (abbrev-symbol clean-name julia-latexsub-abbrev-table))
+                   (end (+ beg (length clean-name))))
           (abbrev-insert symb name beg end)))
     #'ignore))