patch 8.1.1562: popup window not always redrawn after popup_setoptions()

Problem:    Popup window not always redrawn after popup_setoptions().
Solution:   Force a redraw.
diff --git a/src/popupwin.c b/src/popupwin.c
index d777ae5..b1c9840 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -1449,6 +1449,7 @@
     apply_move_options(wp, dict);
     apply_general_options(wp, dict);
 
+    popup_mask_refresh = TRUE;
     popup_adjust_position(wp);
 }