patch 8.0.1450: GUI: endless loop when stopping cursor blinking

Problem:    Endless loop when gui_mch_stop_blink() is called while blink_state
            is BLINK_OFF. (zdohnal)
Solution:   Avoid calling gui_update_cursor() recursively.
diff --git a/src/gui_x11.c b/src/gui_x11.c
index ee48fb3..34d584e 100644
--- a/src/gui_x11.c
+++ b/src/gui_x11.c
@@ -2746,7 +2746,7 @@
 	    if (gui.in_focus)
 		gui_mch_start_blink();
 	    else
-		gui_mch_stop_blink();
+		gui_mch_stop_blink(TRUE);
 	    focus = gui.in_focus;
 	}
 
@@ -3105,14 +3105,14 @@
  * Stop the cursor blinking.  Show the cursor if it wasn't shown.
  */
     void
-gui_mch_stop_blink(void)
+gui_mch_stop_blink(int may_call_gui_update_cursor)
 {
     if (blink_timer != (XtIntervalId)0)
     {
 	XtRemoveTimeOut(blink_timer);
 	blink_timer = (XtIntervalId)0;
     }
-    if (blink_state == BLINK_OFF)
+    if (blink_state == BLINK_OFF && may_call_gui_update_cursor)
 	gui_update_cursor(TRUE, FALSE);
     blink_state = BLINK_NONE;
 }