flac: patch seeking bug

flac: patch seeking bug

While working on audiofile recipe from meta-oe, a test that is using flac
to convert a flac file failed with this particular version of the recipe.

Bisecting the issue pointed to a code snippet that later was modifed with the
patch that is introduced here: in version 1.3.4 there is a bug with seeking
in flac files, returning incorrect pointers.

This backported patch fixes this (and fixes the ptest also, that triggered this).

Signed-off-by: Gyorgy Sarvari <skandigraun@gmail.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>