obs-outputs: Fix bug (headers not always sent)

If a disconnection occurs, the sent_headers would still be set to true,
and when a reconnect occurs, it would not send the headers again.

plugins/obs-outputs/rtmp-stream.c

@@ -264,6 +264,7 @@ static void *send_thread(void *data)
 	}
 
 	stream->active = false;
+	stream->sent_headers = false;
 	return NULL;
 }