lavc/hevcdec: Update slice index before hwaccel decode slice

Otherwise, slice index will never update for hwaccel decode, and slice
RPL will be always overlap into first one which use slice index to construct.

Fixes hwaccel decoding after 47d34ba7fb

Signed-off-by: Fei Wang <fei.w.wang@intel.com>

libavcodec/hevc/hevcdec.c

@@ -2765,6 +2765,9 @@ static int decode_slice_data(HEVCContext *s, const H2645NAL *nal, GetBitContext
     const HEVCPPS *pps = s->pps;
     int ret;
 
+    if (!s->sh.first_slice_in_pic_flag)
+        s->slice_idx += !s->sh.dependent_slice_segment_flag;
+
     if (!s->sh.dependent_slice_segment_flag && s->sh.slice_type != HEVC_SLICE_I) {
         ret = ff_hevc_slice_rpl(s);
         if (ret < 0) {
@@ -2802,8 +2805,6 @@ static int decode_slice_data(HEVCContext *s, const H2645NAL *nal, GetBitContext
     s->local_ctx[0].tu.cu_qp_offset_cb = 0;
     s->local_ctx[0].tu.cu_qp_offset_cr = 0;
 
-    s->slice_idx += !s->sh.dependent_slice_segment_flag;
-
     if (s->avctx->active_thread_type == FF_THREAD_SLICE  &&
         s->sh.num_entry_point_offsets > 0                &&
         pps->num_tile_rows == 1 && pps->num_tile_columns == 1)