patch 8.1.1422: popup_getoptions() not implemented yet

Problem:    Popup_getoptions() not implemented yet.
Solution:   Implement it. (closes #4452)
diff --git a/src/proto/popupwin.pro b/src/proto/popupwin.pro
index 83b5f2c..7337457 100644
--- a/src/proto/popupwin.pro
+++ b/src/proto/popupwin.pro
@@ -10,5 +10,6 @@
 void close_all_popups(void);
 void ex_popupclear(exarg_T *eap);
 void f_popup_move(typval_T *argvars, typval_T *rettv);
+void f_popup_getoptions(typval_T *argvars, typval_T *rettv);
 void f_popup_getposition(typval_T *argvars, typval_T *rettv);
 /* vim: set ft=c : */