oggdec: simplify start time calculation code.

Also slightly more correct behaviour in case streams_left for
some reason is 0 from the start.
Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavformat/oggdec.c

@@ -526,9 +526,10 @@ static int ogg_get_length(AVFormatContext *s)
     avio_seek (s->pb, s->data_offset, SEEK_SET);
     ogg_reset(s);
     i = -1;
-    while (!ogg_packet(s, &i, NULL, NULL, NULL)) {
-        if(i>=0) {
-        int64_t pts = ogg_calc_pts(s, i, NULL);
+    while (streams_left > 0 && !ogg_packet(s, &i, NULL, NULL, NULL)) {
+        int64_t pts;
+        if (i < 0) continue;
+        pts = ogg_calc_pts(s, i, NULL);
         if (pts != AV_NOPTS_VALUE && s->streams[i]->start_time == AV_NOPTS_VALUE && !ogg->streams[i].got_start){
             s->streams[i]->duration -= pts;
             ogg->streams[i].got_start= 1;
@@ -537,9 +538,6 @@ static int ogg_get_length(AVFormatContext *s)
             ogg->streams[i].got_start= 1;
             streams_left--;
         }
-        }
-            if(streams_left<=0)
-                break;
     }
     ogg_restore (s, 0);