ALStream: Fix sometimes not unqueuing all buffers before play

Very rarely rogue buffers would remain and play on loop on song
switch because we only ever cleared processed, not queued, buffers
from the source.

The correct way to completely clear a source's queue is to
simply attach a null buffer to it.

src/al-util.h

@@ -133,6 +133,11 @@ namespace Source
 		return buffer;
 	}
 
+	inline void clearQueue(Source::ID id)
+	{
+		attachBuffer(id, Buffer::ID(0));
+	}
+
 	inline ALint getInteger(Source::ID id, ALenum prop)
 	{
 		ALint value;

src/alstream.cpp

@@ -57,8 +57,7 @@ ALStream::~ALStream()
 {
 	close();
 
-	clearALQueue();
-
+	AL::Source::clearQueue(alSrc);
 	AL::Source::del(alSrc);
 
 	for (int i = 0; i < STREAM_BUFS; ++i)
@@ -228,7 +227,7 @@ void ALStream::stopStream()
 
 void ALStream::startStream(float offset)
 {
-	clearALQueue();
+	AL::Source::clearQueue(alSrc);
 
 	preemptPause = false;
 	streamInited = false;
@@ -292,15 +291,6 @@ void ALStream::checkStopped()
 	state = Stopped;
 }
 
-void ALStream::clearALQueue()
-{
-	/* Unqueue all buffers */
-	ALint queuedBufs = AL::Source::getProcBufferCount(alSrc);
-
-	while (queuedBufs--)
-		AL::Source::unqueueBuffer(alSrc);
-}
-
 /* thread func */
 void ALStream::streamData()
 {

src/alstream.h

@@ -112,7 +112,6 @@ private:
 	void resumeStream();
 
 	void checkStopped();
-	void clearALQueue();
 
 	/* thread func */
 	void streamData();