SCI: kDoAudio stops samples played with kDoSound #2792
This fixes subtle sound bugs in SCI16 games with speech. The SQ4CD introduction has at least two:
In both of these cases, the digital sample should have stopped as soon as speech started.
In SSCI, digital samples are handled by kDoAudio. If a digital sample is played with kDoSound then SSCI just calls kDoAudio and it still does the work. When kDoAudio plays, it first stops any samples that it already played.
In ScummVM, all sounds played with kDoSound are handled separately from kDoAudio, even if they're samples, so an extra step is needed for our kDoAudio to stop all samples as SSCI does.
[ Ignore the name of my branch; I wasn't paying attention ]