Calling consume_all() is illegal in the producer thread.

Fixes bogus Delay() results at the start of playback, because Delay()
thinks the output is paused.

Fixes a bogus assertion failure (which can now be removed).

Instead of generating silence, do nothing, don't waste CPU time.

This code is complicated - and broken: the producer thread is not
allowed to call consumer methods.  Also the code is not necessary
because this plugin implements Interrupt().

OpenDevice was a confusing name because it does not actually open a
device.

Postpone the Start() call until there is something to be played.

This finishes problems which occur early in the WasapiOutputThread;
previously, the error was ignored and the output blocked forever
without doing anything (and without reporting the error).

This is duplicate; this has already been done in Close().

This is pointless; the method cannot be called again anyway.

It is pointless to let WasapiOutputThread wait for the
CheckException() call.

If an exception has been caught, the method cannot continue playback,
therefore it doesn't make sense to have the "catch" block inside the
"while" block (and not break the loop after catching an exception).

The current Drain() implementation does what Cancel() should do; it
does not wait for completion, but instead discards the buffer.