patch 8.1.1997: no redraw after a popup window filter is invoked

Problem:    No redraw after a popup window filter is invoked.
Solution:   Redraw if needed.
diff --git a/src/popupwin.c b/src/popupwin.c
index 226232d..1fb72bb 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -2802,6 +2802,8 @@
 		&& (wp->w_filter_mode & state) != 0)
 	    res = invoke_popup_filter(wp, c);
 
+    if (must_redraw)
+	redraw_after_callback(FALSE);
     recursive = FALSE;
     KeyTyped = save_KeyTyped;
     return res;