patch 8.1.1998: redraw even when no popup window filter was invoked

Problem:    Redraw even when no popup window filter was invoked.
Solution:   Only redraw when must_redraw was set to a larger value.
diff --git a/src/popupwin.c b/src/popupwin.c
index 1fb72bb..7fb9792 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -2779,6 +2779,7 @@
     win_T	*wp;
     int		save_KeyTyped = KeyTyped;
     int		state;
+    int		was_must_redraw = must_redraw;
 
     if (recursive)
 	return FALSE;
@@ -2802,7 +2803,7 @@
 		&& (wp->w_filter_mode & state) != 0)
 	    res = invoke_popup_filter(wp, c);
 
-    if (must_redraw)
+    if (must_redraw > was_must_redraw)
 	redraw_after_callback(FALSE);
     recursive = FALSE;
     KeyTyped = save_KeyTyped;