avformat/img2dec: initialize pkt->pos for image pipes

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

libavformat/img2dec.c

@@ -450,6 +450,9 @@ int ff_img_read_packet(AVFormatContext *s1, AVPacket *pkt)
         pkt->pts      = s->pts;
     }
 
+    if (s->is_pipe)
+        pkt->pos = avio_tell(f[0]);
+
     pkt->size = 0;
     for (i = 0; i < 3; i++) {
         if (f[i]) {

tests/ref/fate/exif-image-tiff

@@ -9,7 +9,7 @@ best_effort_timestamp=0
 best_effort_timestamp_time=0.000000
 pkt_duration=1
 pkt_duration_time=0.040000
-pkt_pos=N/A
+pkt_pos=0
 pkt_size=67604
 width=200
 height=112

tests/ref/fate/exif-image-webp

@@ -9,7 +9,7 @@ best_effort_timestamp=0
 best_effort_timestamp_time=0.000000
 pkt_duration=1
 pkt_duration_time=0.040000
-pkt_pos=N/A
+pkt_pos=0
 pkt_size=39276
 width=400
 height=225