oggdec: Make sure start time correction is applied once to each stream

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

libavformat/oggdec.h

@@ -75,6 +75,7 @@ struct ogg_stream {
     int incomplete; ///< whether we're expecting a continuation in the next page
     int page_end;   ///< current packet is the last one completed in the page
     int keyframe_seek;
+    int got_start;
     void *private;
 };