patch 8.2.2341: expresison command line completion incomplete after "g:"

Problem:    Expresison command line completion shows variables but not
            functions after "g:". (Gary Johnson)
Solution:   Prefix "g:" when needed to a global function.
diff --git a/src/proto/evalvars.pro b/src/proto/evalvars.pro
index c597ca3..0861a88 100644
--- a/src/proto/evalvars.pro
+++ b/src/proto/evalvars.pro
@@ -26,6 +26,7 @@
 int do_unlet(char_u *name, int forceit);
 void item_lock(typval_T *tv, int deep, int lock, int check_refcount);
 void del_menutrans_vars(void);
+char_u *cat_prefix_varname(int prefix, char_u *name);
 char_u *get_user_var_name(expand_T *xp, int idx);
 char *get_var_special_name(int nr);
 dict_T *get_globvar_dict(void);