Rework source updates, do clean stopping of streaming sources once they end. (bug #295)

src/modules/audio/null/Source.cpp

@@ -77,8 +77,9 @@ namespace null
 		return true;
 	}
 
-	void Source::update()
+	bool Source::update()
 	{
+		return false;
 	}
 
 	void Source::setPitch(float pitch)

src/modules/audio/null/Source.h

@@ -52,7 +52,7 @@ namespace null
 		virtual bool isStopped() const;
 		virtual bool isPaused() const;
 		virtual bool isFinished() const;
-		virtual void update();
+		virtual bool update();
 		virtual void setPitch(float pitch);
 		virtual float getPitch() const;
 		virtual void setVolume(float volume);