Do not decode RV30 files if the extradata is too small

Signed-off-by: Diego Biurrun <diego@biurrun.de>

libavcodec/rv30.c

@@ -256,6 +256,7 @@ static av_cold int rv30_decode_init(AVCodecContext *avctx)
     if(avctx->extradata_size - 8 < (r->rpr - 1) * 2){
         av_log(avctx, AV_LOG_ERROR, "Insufficient extradata - need at least %d bytes, got %d\n",
                6 + r->rpr * 2, avctx->extradata_size);
+        return EINVAL;
     }
     r->parse_slice_header = rv30_parse_slice_header;
     r->decode_intra_types = rv30_decode_intra_types;