avcodec/vp3: ensure header is parsed successfully before tables

Fixes assertion failure
Fixes: 266ee543812e934f7b4a72923a2701d4/signal_sigabrt_7ffff6ae7cc9_7322_85218d61759d461bdf7387180e8000c9.ogg

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/vp3.c

@@ -131,7 +131,7 @@ static const uint8_t hilbert_offset[16][2] = {
 
 typedef struct Vp3DecodeContext {
     AVCodecContext *avctx;
-    int theora, theora_tables;
+    int theora, theora_tables, theora_header;
     int version;
     int width, height;
     int chroma_x_shift, chroma_y_shift;
@@ -2258,6 +2258,7 @@ static int theora_decode_header(AVCodecContext *avctx, GetBitContext *gb)
     int ret;
     AVRational fps, aspect;
 
+    s->theora_header = 0;
     s->theora = get_bits_long(gb, 24);
     av_log(avctx, AV_LOG_DEBUG, "Theora bitstream version %X\n", s->theora);
 
@@ -2363,6 +2364,7 @@ static int theora_decode_header(AVCodecContext *avctx, GetBitContext *gb)
         avctx->color_trc  = AVCOL_TRC_BT709;
     }
 
+    s->theora_header = 1;
     return 0;
 }
 
@@ -2371,6 +2373,9 @@ static int theora_decode_tables(AVCodecContext *avctx, GetBitContext *gb)
     Vp3DecodeContext *s = avctx->priv_data;
     int i, n, matrices, inter, plane;
 
+    if (!s->theora_header)
+        return AVERROR_INVALIDDATA;
+
     if (s->theora >= 0x030200) {
         n = get_bits(gb, 3);
         /* loop filter limit values table */