engines/windowsaio: fix silly thinky on IO thread creation

I inadvertently made the setup fail unless the affinity option was
set, the intent was obviously to only run the affinitization if we
asked for it.

Fixes: 09c1aa8b3227 ("engines/windowsaio: only set IOCP thread affinity if specified")
Signed-off-by: Jens Axboe <axboe@kernel.dk>