[core] check fcntl O_APPEND succeeds w/ mkstemp()

src/chunk.c

@@ -481,8 +481,12 @@ static chunk *chunkqueue_get_append_tempfile(chunkqueue *cq) {
 		return NULL;
 	}
 
+	if (0 != fcntl(fd, F_SETFL, fcntl(fd, F_GETFL, 0) | O_APPEND)) {
+		close(fd);
+		buffer_free(template);
+		return NULL;
+	}
 	fd_close_on_exec(fd);
-	(void)fcntl(fd, F_SETFL, fcntl(fd, F_GETFL, 0) | O_APPEND);
 
 	c = chunkqueue_get_unused_chunk(cq);
 	c->type = FILE_CHUNK;