patch 8.1.1453: popup window "moved" property not implemented yet

Problem:    Popup window "moved" property not implemented yet.
Solution:   Implement it.
diff --git a/src/proto/popupwin.pro b/src/proto/popupwin.pro
index 24a1023..a50e7b7 100644
--- a/src/proto/popupwin.pro
+++ b/src/proto/popupwin.pro
@@ -17,4 +17,5 @@
 void popup_reset_handled(void);
 win_T *find_next_popup(int lowest);
 int popup_do_filter(int c);
+void popup_check_cursor_pos(void);
 /* vim: set ft=c : */