patch 8.1.1441: popup window filter not yet implemented

Problem:    Popup window filter not yet implemented.
Solution:   Implement the popup filter.
diff --git a/src/getchar.c b/src/getchar.c
index 02535ce..80e98ec 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -1801,6 +1801,10 @@
 	ui_remove_balloon();
     }
 #endif
+#ifdef FEAT_TEXT_PROP
+    if (popup_do_filter(c))
+	c = K_IGNORE;
+#endif
 
     return c;
 }