oggdec: resync from the last page.

Previously we re synced from where we where which cam lead
to loosing pages.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/oggdec.h

@@ -100,6 +100,7 @@ struct ogg {
     int nstreams;
     int headers;
     int curidx;
+    int64_t page_pos;                   ///< file offset of the current page
     struct ogg_state *state;
 };