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.

Fixes those programs on Windows.

MSDN documentation suggests always passing this flag to reduce
overhead for an "obsolete technology".

None of the current FormatHResultError() callers need the format string.

Parameters should better be captured.  This removes some complexity
from Async().

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1102

Stop early, don't try more formats if it is clear that we have no
chance.

Fixes assertion failure in the Thread destructor.

Fixes crash due to std::stoul() throwing std::invalid_argument.