lavc/videotoolbox: drop HEVC cropping from start_frame rather than end_frame

HEVCContext.output_frame will be removed in following commits.

Reported-By: Max Bykov

libavcodec/videotoolbox.c

@@ -1053,6 +1053,14 @@ static int videotoolbox_hevc_start_frame(AVCodecContext *avctx,
                                          const uint8_t *buffer,
                                          uint32_t size)
 {
+    HEVCContext *h = avctx->priv_data;
+    AVFrame *frame = h->cur_frame->f;
+
+    frame->crop_right  = 0;
+    frame->crop_left   = 0;
+    frame->crop_top    = 0;
+    frame->crop_bottom = 0;
+
     return 0;
 }
 
@@ -1079,11 +1087,6 @@ static int videotoolbox_hevc_end_frame(AVCodecContext *avctx)
     VTContext *vtctx = avctx->internal->hwaccel_priv_data;
     int ret;
 
-    h->output_frame->crop_right = 0;
-    h->output_frame->crop_left = 0;
-    h->output_frame->crop_top = 0;
-    h->output_frame->crop_bottom = 0;
-
     ret = ff_videotoolbox_common_end_frame(avctx, frame);
     vtctx->bitstream_size = 0;
     return ret;