proper check for valid pva_pts

Originally committed as revision 11429 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/pva.c

@@ -144,7 +144,7 @@ recover:
         return AVERROR(EIO);
 
     pkt->stream_index = streamid - 1;
-    if (pva_pts)
+    if (pva_pts != AV_NOPTS_VALUE)
         pkt->pts = pva_pts;
 
     return ret;