SoundSystem: fixed stream sounds playback bug.

When stream sounds (i.e. buffers created with SoundHandler::loadStreamSounds)
were played until EOF, the file get pointer was not being relocated to the
beginning of the file.
This caused failures in later calls to update and/or play.

Fix includes:
	· new boolean member for the SSoundSource class: mFileFinished
	· change of "pcmData" array in SoundBuffer class to StackVector type
	· updated SoundBuffer::filler() methods for this new array type
	· change to end() method of StackVector template