thumbnail: Check rename for errors

thumbnail.c

@@ -100,7 +100,8 @@ int main(int argc, char *argv[])
 	if (av_write_trailer(mux))
 		goto fail;
 	avio_closep(&mux->pb);
-	rename(tmp, dest);
+	if (rename(tmp, dest))
+		goto fail;
 	unlink(tmp);
 	ping_job(jobid, "finished", "{\"log\": \"%s\"}", get_avlogbuf());
 	return 0;