EMI: Less restrictive parameter check for PlaySound()

Use default volume in case the volume parameter is omitted
or of the wrong type (may happen for the sounds of Murray
on Jambalaya Island).
EMI: Don't restart tracks via EMISound::setMusicState

When using the rowboat in act 2, setMusicState is called very
frequently to update the correct music based on the position
of the boat. This causes a continously repetition of the first
view seconds of the tracks.

setMusicState() should not restart the track in case it is already
playing.
EMI: Implement ImStateHasLooped

The implementation is necessary to switch between various music tracks
in Knuttin Town.