Do not set audio_resample to 0 if audio_sync_method is > 1.

If audio_sync_method is >1 the resampler is used for audio drift
compensation, and do_audio_out() was causing an assert failure because
audio_resample was not set.

Fix issue 2516, which was introduced by SVN r25939.

Signed-off-by: Mans Rullgard <mans@mansr.com>