patch 8.1.1770: cannot get the window ID of the popup preview window
Problem: Cannot get the window ID of the popup preview window.
Solution: Add popup_getpreview().
diff --git a/src/proto/popupwin.pro b/src/proto/popupwin.pro
index 605575b..04825cc 100644
--- a/src/proto/popupwin.pro
+++ b/src/proto/popupwin.pro
@@ -42,6 +42,7 @@
void update_popups(void (*win_update)(win_T *wp));
int set_ref_in_popups(int copyID);
win_T *popup_find_preview_window(void);
+void f_popup_getpreview(typval_T *argvars, typval_T *rettv);
int popup_is_popup(win_T *wp);
int popup_create_preview_window(void);
void popup_close_preview(void);