oggdec filter improvements.

Try to open the ogg vorbis callbacks as soon as possible rather
than waiting until the input buffer reaches the given initial buffer
size. If that fails, try again later when more data is available but
fail if the input buffer size is larger than the initial buffer size
and we can still not open the ov callbacks.

Also, if a hole was detected, likely because we started streaming
in the middle of the file, add an additional delay to avoid buffer
underruns.