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/ex_docmd.c b/src/ex_docmd.c
index c7b57ba..477d140 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -3311,7 +3311,7 @@
 find_ex_command(
 	exarg_T *eap,
 	int	*full UNUSED,
-	int	(*lookup)(char_u *, size_t, cctx_T *) UNUSED,
+	int	(*lookup)(char_u *, size_t, int cmd, cctx_T *) UNUSED,
 	cctx_T	*cctx UNUSED)
 {
     int		len;
@@ -3430,7 +3430,7 @@
 			|| *eap->cmd == '&'
 			|| *eap->cmd == '$'
 			|| *eap->cmd == '@'
-			|| lookup(eap->cmd, p - eap->cmd, cctx) == OK)
+			|| lookup(eap->cmd, p - eap->cmd, TRUE, cctx) == OK)
 		{
 		    eap->cmdidx = CMD_var;
 		    return eap->cmd;
@@ -3449,7 +3449,7 @@
 	// If it is an ID it might be a variable with an operator on the next
 	// line, if the variable exists it can't be an Ex command.
 	if (p > eap->cmd && ends_excmd(*skipwhite(p))
-		&& (lookup(eap->cmd, p - eap->cmd, cctx) == OK
+		&& (lookup(eap->cmd, p - eap->cmd, TRUE, cctx) == OK
 		    || (ASCII_ISALPHA(eap->cmd[0]) && eap->cmd[1] == ':')))
 	{
 	    eap->cmdidx = CMD_eval;