patch 8.2.2603: Vim9: no effect if user command is also a function

Problem:    Vim9: no effect if user command is also a function.
Solution:   Check for paren following. (closes #7960)
diff --git a/src/proto/ex_docmd.pro b/src/proto/ex_docmd.pro
index dcd9f39..9ac8eaf 100644
--- a/src/proto/ex_docmd.pro
+++ b/src/proto/ex_docmd.pro
@@ -13,7 +13,7 @@
 int parse_cmd_address(exarg_T *eap, char **errormsg, int silent);
 int checkforcmd(char_u **pp, char *cmd, int len);
 char_u *skip_option_env_lead(char_u *start);
-char_u *find_ex_command(exarg_T *eap, int *full, int (*lookup)(char_u *, size_t, cctx_T *), cctx_T *cctx);
+char_u *find_ex_command(exarg_T *eap, int *full, int (*lookup)(char_u *, size_t, int cmd, cctx_T *), cctx_T *cctx);
 int modifier_len(char_u *cmd);
 int cmd_exists(char_u *name);
 void f_fullcommand(typval_T *argvars, typval_T *rettv);