avcodec/nvdec: reset bitstream_len/nb_slices when resetting bitstream pointer

libavcodec/nvdec.c

@@ -664,6 +664,8 @@ int ff_nvdec_simple_end_frame(AVCodecContext *avctx)
     NVDECContext *ctx = avctx->internal->hwaccel_priv_data;
     int ret = ff_nvdec_end_frame(avctx);
     ctx->bitstream = NULL;
+    ctx->bitstream_len = 0;
+    ctx->nb_slices = 0;
     return ret;
 }