avcodec/h264_slice: Fix uninitialized variable

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

libavcodec/h264_slice.c

@@ -1434,13 +1434,13 @@ int ff_h264_decode_slice_header(H264Context *h, H264SliceContext *sl)
     }
 
     sl->mb_mbaff       = 0;
+    mb_aff_frame       = 0;
     last_mb_aff_frame  = h->mb_aff_frame;
     last_pic_structure = h->picture_structure;
     last_pic_droppable = h->droppable;
     droppable          = h->nal_ref_idc == 0;
     if (h->sps.frame_mbs_only_flag) {
         picture_structure = PICT_FRAME;
-        mb_aff_frame      = 0;
     } else {
         if (!h->sps.direct_8x8_inference_flag && slice_type == AV_PICTURE_TYPE_B) {
             av_log(h->avctx, AV_LOG_ERROR, "This stream was generated by a broken encoder, invalid 8x8 inference\n");