patch 8.1.2335: error message for function arguments may use NULL pointer

Problem:    Error message for function arguments may use NULL pointer.
            (Coverity)
Solution:   Use the original function name.
diff --git a/src/evalfunc.c b/src/evalfunc.c
index b374d55..6a9f9d6 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -2536,7 +2536,7 @@
 		    arg_idx = 0;
 		else if (list->lv_len > MAX_FUNC_ARGS)
 		{
-		    emsg_funcname((char *)e_toomanyarg, name);
+		    emsg_funcname((char *)e_toomanyarg, s);
 		    vim_free(name);
 		    goto theend;
 		}