patch 8.1.1641: garbage collection may run at a wrong moment

Problem:    Garbage collection may run at a wrong moment. (Trygve Aaberge)
Solution:   Postpone garbage collection while parsing messages. (closes #4620)

src/misc2.c

@@ -4444,12 +4444,19 @@ parse_queued_messages(void)
 {
     win_T   *old_curwin = curwin;
     int	    i;
+    int	    save_may_garbage_collect = may_garbage_collect;
 
     // Do not handle messages while redrawing, because it may cause buffers to
     // change or be wiped while they are being redrawn.
     if (updating_screen)
 	return;
 
+    // may_garbage_collect is set in main_loop() to do garbage collection when
+    // blocking to wait on a character.  We don't want that while parsing
+    // messages, a callback may invoke vgetc() while lists and dicts are in use
+    // in the call stack.
+    may_garbage_collect = FALSE;
+
     // Loop when a job ended, but don't keep looping forever.
     for (i = 0; i < MAX_REPEAT_PARSE; ++i)
     {
@@ -4485,6 +4492,8 @@ parse_queued_messages(void)
 	break;
     }
 
+    may_garbage_collect = save_may_garbage_collect;
+
     // If the current window changed we need to bail out of the waiting loop.
     // E.g. when a job exit callback closes the terminal window.
     if (curwin != old_curwin)

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1641,
 /**/
     1640,
 /**/