Simplify prerun() in the case where there are no arguments. Can't do -I or -J

substitution if `utility' is not specified and we're using the buildin echo;
It has no arguments for us to abuse.

usr.bin/xargs/xargs.c

@@ -393,7 +393,7 @@ prerun(int argc, char **argv)
 
 	repls = Rflag;
 
-	if (repls == 0) {
+	if (argc == 0 || repls == 0) {
 		*xp = NULL;
 		run(argv);
 		return;