Fix handling of holes again.

It is possible for us to buffer multiple out-of-sequence pages with no packets on them before getting one that does have packets. In this case, libogg will report each hole in the page sequence numbers separately. Since we were only checking for the actual packets once after encountering a hole, if the total number of holes was even, we could exit op_fetch_and_process_page() with valid packets still in the libogg buffer. Then, if the next page had a lot of packets, we might wind up with a total of more than 255 of them, overflowing our stack buffer for their durations. That's bad.

Instead, make sure we always drain all hole reports from libogg any time we encounter one, to ensure we get the actual packets behind it.

Thanks to Felicia Lim for the report.