Wasapi output plugin won't start playing after being paused

The cause is that the scope guard in the WASAPI work thread
(WasapiOutputPlugin.cxx, function WasapiOutputThread::Work(), in the
while (true) loop) is set up too 'late' in the execution. There is one
condition ("if (data_in_frames >= buffer_size_in_frames)") when it is
hit, the loop will continue without executing the scope guard. This
scope guard is responsible for emptying the buffer again, and if the
buffer is not emptied, the above mentioned condition will stay true.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1451

A few exceptions are needed for sources which include COM header
(directly or indirectly).

This fixes lots of shadow warnings, see
https://github.com/MusicPlayerDaemon/MPD/issues/1150

"%lu" is portable - it works with both POSIX and Microsoft flavors.

Fixes a part of https://github.com/MusicPlayerDaemon/MPD/issues/1150

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.