matroskadec: validate audio channels and bitdepth

In the TTA extradata re-construction the values are written with
avio_wl16 and if they don't fit into uint16_t, this triggers an
av_assert2 in avio_w8.
Reviewed-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

libavformat/matroskadec.c

@@ -1889,6 +1889,18 @@ static int matroska_parse_tracks(AVFormatContext *s)
                               NULL, NULL, NULL, NULL);
             avio_write(&b, "TTA1", 4);
             avio_wl16(&b, 1);
+            if (track->audio.channels > UINT16_MAX ||
+                track->audio.bitdepth > UINT16_MAX) {
+                av_log(matroska->ctx, AV_LOG_WARNING,
+                       "Too large audio channel number %"PRIu64
+                       " or bitdepth %"PRIu64". Skipping track.\n",
+                       track->audio.channels, track->audio.bitdepth);
+                av_freep(&extradata);
+                if (matroska->ctx->error_recognition & AV_EF_EXPLODE)
+                    return AVERROR_INVALIDDATA;
+                else
+                    continue;
+            }
             avio_wl16(&b, track->audio.channels);
             avio_wl16(&b, track->audio.bitdepth);
             if (track->audio.out_samplerate < 0 || track->audio.out_samplerate > INT_MAX)