img2enc: show first 4 bytes if a malformed jpeg2000 codestream is detected

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

libavformat/img2.c

@@ -442,7 +442,7 @@ static int write_packet(AVFormatContext *s, AVPacket *pkt)
                      (!st->codec->extradata_size &&
                       AV_RL32(pkt->data+4) != MKTAG('j','P',' ',' '))){ // signature
             error:
-                av_log(s, AV_LOG_ERROR, "malformated jpeg2000 codestream\n");
+                av_log(s, AV_LOG_ERROR, "malformated jpeg2000 codestream %X\n", AV_RB32(pkt->data));
                 return -1;
             }
         }