Merge commit 'b8d7f318'

* commit 'b8d7f318':
  matroskadec: fix crash when parsing invalid mkv
Merged-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/matroskadec.c

@@ -2080,8 +2080,12 @@ static int matroska_read_header(AVFormatContext *s)
     matroska->cues_parsing_deferred = 1;
 
     /* First read the EBML header. */
-    if (ebml_parse(matroska, ebml_syntax, &ebml) ||
-        ebml.version         > EBML_VERSION      ||
+    if (ebml_parse(matroska, ebml_syntax, &ebml) || !ebml.doctype) {
+        av_log(matroska->ctx, AV_LOG_ERROR, "EBML header parsing failed\n");
+        ebml_free(ebml_syntax, &ebml);
+        return AVERROR_INVALIDDATA;
+    }
+    if (ebml.version         > EBML_VERSION      ||
         ebml.max_size        > sizeof(uint64_t)  ||
         ebml.id_length       > sizeof(uint32_t)  ||
         ebml.doctype_version > 3                 ||