avcodec/mjpegdec: Check for pixfmtid 0x42111100 || 0x24111100 with more than 8 bits

These cases are not supported yet

Fixes assertion failure
Fixes: signal_sigabrt_7ffff6ac7bb9_1_cov_1553101927_00.jpg
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mjpegdec.c

@@ -533,8 +533,12 @@ int ff_mjpeg_decode_sof(MJpegDecodeContext *s)
         else              s->avctx->pix_fmt = AV_PIX_FMT_YUV420P16;
         s->avctx->color_range = s->cs_itu601 ? AVCOL_RANGE_MPEG : AVCOL_RANGE_JPEG;
         if (pix_fmt_id == 0x42111100) {
+            if (s->bits > 8)
+                goto unk_pixfmt;
             s->upscale_h = 6;
         } else if (pix_fmt_id == 0x24111100) {
+            if (s->bits > 8)
+                goto unk_pixfmt;
             s->upscale_v = 6;
         }
         break;