Add source:isPaused() (enhancement #141)

src/modules/audio/null/Source.h

@@ -50,6 +50,7 @@ namespace null
 		virtual void resume();
 		virtual void rewind();
 		virtual bool isStopped() const;
+		virtual bool isPaused() const;
 		virtual bool isFinished() const;
 		virtual void update();
 		virtual void setPitch(float pitch);