oggdec: Fix EOF handling on repositioning.

oggdec: Fix EOF handling on repositioning.

If playback starts near the end of the file, it might happen that (a)
the read callback consumes all the remaining part in one go (so the
node status is BTR_EOF) and (b) the last ov_read() returned OV_HOLE.

(b) makes the decoder wait for more data which will never arrive due to
(a). Currently we error out without playing the last part of the file.

This patch makes ogg_post_select() return an error only if additionally
fn->min_iqs == 0, which indicates we did not hit OV_HOLE during the
last ov_read().