fixed compiler warning by making a function void and not bool (anhyway it didn't return anything, and nothing checked for a return value when calling it)

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/trunk/supertuxkart@2710 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/audio/music.hpp

@@ -30,7 +30,7 @@ public:
     virtual bool stopMusic   ()                            = 0;
     virtual bool pauseMusic  ()                            = 0;
     virtual bool resumeMusic ()                            = 0;
-    virtual bool volumeMusic (float gain)                  = 0;
+    virtual void volumeMusic (float gain)                  = 0;
     virtual void updateFading(float percent)               = 0;
     virtual void updateFaster(float percent, float pitch)  = 0;
     virtual void update      ()                            = 0;

src/audio/music_ogg.cpp

@@ -207,7 +207,7 @@ bool MusicOggStream::resumeMusic()
 }   // resumeMusic
 
 //-----------------------------------------------------------------------------
-bool MusicOggStream::volumeMusic(float gain)
+void MusicOggStream::volumeMusic(float gain)
 {
     alSourcef(m_soundSource, AL_GAIN, gain);
 } // volumeMusic

src/audio/music_ogg.hpp

@@ -55,7 +55,7 @@ public:
     virtual bool stopMusic();
     virtual bool pauseMusic();
     virtual bool resumeMusic();
-    virtual bool volumeMusic (float gain);
+    virtual void volumeMusic (float gain);
 
 protected:
     bool empty();