avcodec/mpeg4videodec: Check for bitstream end in read_quant_matrix_ext()

Fixes: out of array read
Fixes: asff-crash-0e53d0dc491dfdd507530b66562812fbd4c36678

Found-by: Paul Ch <paulcher@icloud.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/mpeg4videodec.c

@@ -2867,11 +2867,13 @@ static int decode_vop_header(Mpeg4DecContext *ctx, GetBitContext *gb)
     return 0;
 }
 
-static void read_quant_matrix_ext(MpegEncContext *s, GetBitContext *gb)
+static int read_quant_matrix_ext(MpegEncContext *s, GetBitContext *gb)
 {
     int i, j, v;
 
     if (get_bits1(gb)) {
+        if (get_bits_left(gb) < 64*8)
+            return AVERROR_INVALIDDATA;
         /* intra_quantiser_matrix */
         for (i = 0; i < 64; i++) {
             v = get_bits(gb, 8);
@@ -2882,6 +2884,8 @@ static void read_quant_matrix_ext(MpegEncContext *s, GetBitContext *gb)
     }
 
     if (get_bits1(gb)) {
+        if (get_bits_left(gb) < 64*8)
+            return AVERROR_INVALIDDATA;
         /* non_intra_quantiser_matrix */
         for (i = 0; i < 64; i++) {
             get_bits(gb, 8);
@@ -2889,6 +2893,8 @@ static void read_quant_matrix_ext(MpegEncContext *s, GetBitContext *gb)
     }
 
     if (get_bits1(gb)) {
+        if (get_bits_left(gb) < 64*8)
+            return AVERROR_INVALIDDATA;
         /* chroma_intra_quantiser_matrix */
         for (i = 0; i < 64; i++) {
             v = get_bits(gb, 8);
@@ -2898,6 +2904,8 @@ static void read_quant_matrix_ext(MpegEncContext *s, GetBitContext *gb)
     }
 
     if (get_bits1(gb)) {
+        if (get_bits_left(gb) < 64*8)
+            return AVERROR_INVALIDDATA;
         /* chroma_non_intra_quantiser_matrix */
         for (i = 0; i < 64; i++) {
             get_bits(gb, 8);
@@ -2905,6 +2913,7 @@ static void read_quant_matrix_ext(MpegEncContext *s, GetBitContext *gb)
     }
 
     next_start_code_studio(gb);
+    return 0;
 }
 
 static void extension_and_user_data(MpegEncContext *s, GetBitContext *gb, int id)