Based on a patch from Vladimir Panteleev

Makes directsound switch to silent playback even when no buffers are
playing, fixes glitching on starting playback from a stopped buffer.

wined3d: Simply use surface_modify_location() in IWineD3DSurfaceImpl_Map() with WINED3DLOCK_DISCARD.

The call to surface_add_dirty_rect() would have taken care of evicting the
other locations anyway, but we really shouldn't be touching the location flags
directly.

This fixes IBasicVideo:GetCurrentImage.

Accidentally made a worse leak by plugging a smaller one.

This will fix the hangs caused by trying to play audio/video files for
which the codecs are not enabled in gstreamer.