matroska: don't complain about unknown elements

Matroska is an extensible format - unknown elements must be expected. It
shouldn't complain about such elements to the user either; it'll just
generate noise. The "error_recognition & AV_EF_EXPLODE" is completely,
wrong why would it explode on valid files?

It's still useful for debugging, so the message is left in place with a
higher log level.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/matroskadec.c

@@ -927,9 +927,7 @@ static int ebml_parse_id(MatroskaDemuxContext *matroska, EbmlSyntax *syntax,
         matroska->levels[matroska->num_levels - 1].length == 0xffffffffffffff)
         return 0;  // we reached the end of an unknown size cluster
     if (!syntax[i].id && id != EBML_ID_VOID && id != EBML_ID_CRC32) {
-        av_log(matroska->ctx, AV_LOG_INFO, "Unknown entry 0x%"PRIX32"\n", id);
-        if (matroska->ctx->error_recognition & AV_EF_EXPLODE)
-            return AVERROR_INVALIDDATA;
+        av_log(matroska->ctx, AV_LOG_DEBUG, "Unknown entry 0x%"PRIX32"\n", id);
     }
     return ebml_parse_elem(matroska, &syntax[i], data);
 }