avcodec/dnxhddec: Move mb height check out of non hr branch

Fixes: out of array access
Fixes: poc.dnxhd

Found-by: Bingchang, Liu@VARAS of IIE
Signed-off-by: NMichael Niedermayer <michael@niedermayer.cc>

libavcodec/dnxhddec.c

@@ -298,14 +298,18 @@ static int dnxhd_decode_header(DNXHDContext *ctx, AVFrame *frame,
     if (ctx->mb_height > 68 && ff_dnxhd_check_header_prefix_hr(header_prefix)) {
         ctx->data_offset = 0x170 + (ctx->mb_height << 2);
     } else {
-        if (ctx->mb_height > 68 ||
-            (ctx->mb_height << frame->interlaced_frame) > (ctx->height + 15) >> 4) {
+        if (ctx->mb_height > 68) {
             av_log(ctx->avctx, AV_LOG_ERROR,
                    "mb height too big: %d\n", ctx->mb_height);
             return AVERROR_INVALIDDATA;
         }
         ctx->data_offset = 0x280;
     }
+    if ((ctx->mb_height << frame->interlaced_frame) > (ctx->height + 15) >> 4) {
+        av_log(ctx->avctx, AV_LOG_ERROR,
+                "mb height too big: %d\n", ctx->mb_height);
+        return AVERROR_INVALIDDATA;
+    }
 
     if (buf_size < ctx->data_offset) {
         av_log(ctx->avctx, AV_LOG_ERROR,