MTA was checked in the Open function. As this function is called from libvlc
thread, this implies that a user of libvlc should have its own thread in MTA
which may not be possible for various reasons.
MuteSet, VolumeSet, Play, DeviceSelect, Close callback don't require MTA
Flush, Pause and Start callbacks still require MTA, but as these functions are
called from VLC internal thread this is a lesser issue