mpeg4video_parser: init static tables before use, fix nulll ptr deref

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

libavcodec/mpeg4video_parser.c

@@ -109,6 +109,8 @@ static av_cold int mpeg4video_parse_init(AVCodecParserContext *s)
 {
     struct Mp4vParseContext *pc = s->priv_data;
 
+    ff_mpeg4videodec_static_init();
+
     pc->first_picture = 1;
     pc->enc.quant_precision=5;
     pc->enc.slice_context_count = 1;