patch 8.2.1948: GUI: crash when handling message while closing a window

Problem:    GUI: crash when handling message while closing a window. (Srinath
            Avadhanula)
Solution:   Don't handle message while closing a window. (closes #7250)

src/getchar.c

@@ -2155,7 +2155,8 @@ parse_queued_messages(void)
 
     // Do not handle messages while redrawing, because it may cause buffers to
     // change or be wiped while they are being redrawn.
-    if (updating_screen)
+    // Also bail out when parsing messages was explicitly disabled.
+    if (updating_screen || dont_parse_messages)
 	return;
 
     // If memory allocation fails during startup we'll exit but curbuf or

src/globals.h

@@ -581,6 +581,12 @@ EXTERN int	diff_need_scrollbind INIT(= FALSE);
 // ('lines' and 'rows') must not be changed.
 EXTERN int	updating_screen INIT(= FALSE);
 
+#ifdef MESSAGE_QUEUE
+// While closing windows or buffers messages should not be handled to avoid
+// using invalid windows or buffers.
+EXTERN int	dont_parse_messages INIT(= FALSE);
+#endif
+
 #ifdef FEAT_MENU
 // The root of the menu hierarchy.
 EXTERN vimmenu_T	*root_menu INIT(= NULL);

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1948,
 /**/
     1947,
 /**/

src/window.c

@@ -2569,7 +2569,12 @@ win_close(win_T *win, int free_buf)
 
     // Now we are really going to close the window.  Disallow any autocommand
     // to split a window to avoid trouble.
+    // Also bail out of parse_queued_messages() to avoid it tries to update the
+    // screen.
     ++split_disallowed;
+#ifdef MESSAGE_QUEUE
+    ++dont_parse_messages;
+#endif
 
     // Free the memory used for the window and get the window that received
     // the screen space.
@@ -2626,6 +2631,9 @@ win_close(win_T *win, int free_buf)
     }
 
     --split_disallowed;
+#ifdef MESSAGE_QUEUE
+    --dont_parse_messages;
+#endif
 
     /*
      * If last window has a status line now and we don't want one,