mpeg12: Support decoding dimensions that are a multiple of 4096

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mpeg12.c

@@ -2001,8 +2001,6 @@ static int mpeg1_decode_sequence(AVCodecContext *avctx,
 
     width  = get_bits(&s->gb, 12);
     height = get_bits(&s->gb, 12);
-    if (width <= 0 || height <= 0)
-        return -1;
     s->aspect_ratio_info = get_bits(&s->gb, 4);
     if (s->aspect_ratio_info == 0) {
         av_log(avctx, AV_LOG_ERROR, "aspect ratio has forbidden 0 value\n");
@@ -2312,6 +2310,11 @@ static int decode_chunks(AVCodecContext *avctx,
             break;
 
         case PICTURE_START_CODE:
+            if (s2->width <= 0 || s2->height <= 0) {
+                av_log(avctx, AV_LOG_ERROR, "%dx%d is invalid\n", s2->width, s2->height);
+                return AVERROR_INVALIDDATA;
+            }
+
             if(s->tmpgexs){
                 s2->intra_dc_precision= 3;
                 s2->intra_matrix[0]= 1;