avformat/oggparsedaala: Check duration for AV_NOPTS_VALUE

This avoids an integer overflow
the solution matches oggparsevorbis.c and 45581ed15d

Fixes: 700242

Found-by: Thomas Guilbert <tguilbert@google.com>
Reviewed-by: Rostislav Pehlivanov <atomnuker@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/oggparsedaala.c

@@ -232,7 +232,7 @@ static int daala_packet(AVFormatContext *s, int idx)
         os->lastpts = os->lastdts = daala_gptopts(s, idx, os->granule, NULL) - duration;
         if(s->streams[idx]->start_time == AV_NOPTS_VALUE) {
             s->streams[idx]->start_time = os->lastpts;
-            if (s->streams[idx]->duration)
+            if (s->streams[idx]->duration != AV_NOPTS_VALUE)
                 s->streams[idx]->duration -= s->streams[idx]->start_time;
         }
     }