goruby.c: suppress warning

* goruby.c (goruby_options): check the result of `write(2)` to
  suppress unused-result warning.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47128 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

goruby.c

@@ -32,12 +32,14 @@ goruby_options(int argc, char **argv)
     void *ret;
 
     if ((isatty(0) && isatty(1) && isatty(2)) && (pipe(rw) == 0)) {
+	ssize_t n;
 	infd = dup(0);
+	if (infd < 0) return NULL;
 	dup2(rw[0], 0);
 	close(rw[0]);
-	write(rw[1], cmd, sizeof(cmd) - 1);
+	n = write(rw[1], cmd, sizeof(cmd) - 1);
 	close(rw[1]);
-	ret = ruby_options(argc, argv);
+	ret = n > 0 ? ruby_options(argc, argv) : NULL;
 	dup2(infd, 0);
 	close(infd);
 	return ret;