SoundSystem: unable to fix bug of wav stream files

Same bug of previous commits, but more localized now.
Playback with repeat=on  of OGG and WAV files works fine.
Playback with repeat=off of OGG files works fine.
Playback with repeat=off of WAV files fails with error AL_INVALID_OPERATION,
after starting NUM_SSOURCES (defined in SoundTest.cpp) source playbacks.
Check issue # 207 in MantisBT.