pulse: only fixate when necessary

Check if the format is already fixated before doing a copy and fixate.
The copy can fail so we need to check this.

src/modules/module-protocol-pulse/pending-sample.c

@@ -50,7 +50,6 @@ static void sample_play_ready_reply(void *data, struct client *client, uint32_t
 			message_put(reply,
 				TAG_U32, index,
 				TAG_INVALID);
-
 		client_queue_message(client, reply);
 		ps->replied = true;
 	}