fix: do not set main window postion to center every time when reopening it

Author: tisfeng

Easydict/objc/ViewController/Window/WindowManager/EZWindowManager.m

@@ -667,10 +667,15 @@ - (void)showMainWindowIfNeeded {
     [NSApp setActivationPolicy:activationPolicy];
 
     if (showFlag) {
+        // If the main window does not exist, create it first, and show it center.
+        if (!_mainWindow) {
+            [self.mainWindow center];
+        }
+        [self.mainWindow makeKeyAndOrderFront:nil];
         [self.floatingWindowTypeArray insertObject:@(EZWindowTypeMain) atIndex:0];
 
-        [self.mainWindow center];
-        [self.mainWindow makeKeyAndOrderFront:nil];
+        // TODO: We should record main window showing position, like mini window.
+//        [self showFloatingWindowType:EZWindowTypeMain queryText:nil];
     }
 }