In some situations, "ZUSI 3" has a lot of secondary buffers in the
PLAYING state, but most of these buffers have a really low volume, so
these buffers are multiplied by 0 before mixing (and possibly after
resampling). There can be hundreds of inaudible buffers at the same
time.

In these situations, the dsound mixthread is unable to mix fast enough,
resulting in sound stuttering and generally poor performance.

To resolve this performance issue, skip the mixing (and possibly
resampling) step for all inaudible secondary buffers.
Signed-off-by: Florian Will <florian.will@gmail.com>
Signed-off-by: Andrew Eikum <aeikum@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>