patch 8.2.1237: changing 'completepopup' after opening popup has no effect

Problem:    Changing 'completepopup' after opening a popup has no effect. (Jay
            Sitter)
Solution:   Close the popup when the options are changed. (closes #6471)
diff --git a/src/proto/popupwin.pro b/src/proto/popupwin.pro
index 02cdce3..fe75702 100644
--- a/src/proto/popupwin.pro
+++ b/src/proto/popupwin.pro
@@ -60,6 +60,7 @@
 int popup_create_preview_window(int info);
 void popup_close_preview(void);
 void popup_hide_info(void);
+void popup_close_info(void);
 int popup_win_closed(win_T *win);
 void popup_set_title(win_T *wp);
 void popup_update_preview_title(void);