patch 8.0.1002: unnecessarily updating screen after timer callback

Problem:    Unnecessarily updating screen after timer callback.
Solution:   Check if calling the timer sets must_redraw.

src/screen.c

@@ -445,9 +445,11 @@ redraw_asap(int type)
  * Invoked after an asynchronous callback is called.
  * If an echo command was used the cursor needs to be put back where
  * it belongs. If highlighting was changed a redraw is needed.
+ * If "call_update_screen" is FALSE don't call update_screen() when at the
+ * command line.
  */
     void
-redraw_after_callback(void)
+redraw_after_callback(int call_update_screen)
 {
     ++redrawing_for_callback;
 
@@ -461,7 +463,7 @@ redraw_after_callback(void)
 #ifdef FEAT_WILDMENU
 		&& wild_menu_showing == 0
 #endif
-		)
+		&& call_update_screen)
 	    update_screen(0);
 	/* Redraw in the same position, so that the user can continue
 	 * editing the command. */
@@ -3013,7 +3015,7 @@ win_line(
     int		startrow,
     int		endrow,
     int		nochange UNUSED,	/* not updating for changed text */
-    proftime_T	*syntax_tm)
+    proftime_T	*syntax_tm UNUSED)
 {
     int		col = 0;		/* visual column on screen */
     unsigned	off;			/* offset in ScreenLines/ScreenAttrs */