libavformat/img2dec.c: Add a long_name to the piped image demuxers

This fixes segfaults in gst-libav1.0 compiled against FFmpeg 2.3.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 135ea609ce)

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

libavformat/img2dec.c

@@ -666,6 +666,7 @@ static const AVClass imgname ## _class = {\
 };\
 AVInputFormat ff_image_ ## imgname ## _pipe_demuxer = {\
     .name           = AV_STRINGIFY(imgname) "_pipe",\
+    .long_name      = NULL_IF_CONFIG_SMALL("piped " AV_STRINGIFY(imgname) " sequence"),\
     .priv_data_size = sizeof(VideoDemuxData),\
     .read_probe     = imgname ## _probe,\
     .read_header    = ff_img_read_header,\