avcodec/mjpeg2jpeg_bsf: Check ff_bsf_get_packet success

This fixes ticket #5487 - mjpeg2jpeg bitstream filter causes
segmentation fault with header-less mjpeg.
Signed-off-by: Jan Sebechlebsky <sebechlebskyjan@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/mjpeg2jpeg_bsf.c

@@ -86,6 +86,8 @@ static int mjpeg2jpeg_filter(AVBSFContext *ctx, AVPacket *out)
     uint8_t *output;
 
     ret = ff_bsf_get_packet(ctx, &in);
+    if (ret < 0)
+        return ret;
 
     if (in->size < 12) {
         av_log(ctx, AV_LOG_ERROR, "input is truncated\n");