pulse-server: module-combine-sink: remove unnecessary conditional

After dequeueing the buffer, the code immediately checks if it is NULL,
and never modifies the variable. Therefore there is no need to check
again when the buffer is enqueued.

src/modules/module-protocol-pulse/modules/module-combine-sink.c

@@ -166,7 +166,6 @@ static void capture_process(void *d)
 		pw_stream_queue_buffer(data->streams[i].stream, out);
 	}
 
-	if (in != NULL)
 	pw_stream_queue_buffer(data->sink, in);
 }