fix pointrend inference for empty images

Reviewed By: alexander-kirillov

Differential Revision: D27281355

fbshipit-source-id: cb8a3f0499de4210bdf92bf27670c19d8f8077d7

projects/PointRend/point_rend/mask_head.py

@@ -219,7 +219,7 @@ def _roi_pooler(self, features: List[Tensor], boxes: List[Boxes]):
  roi_features, _ = point_sample_fine_grained_features(
  features_list, features_scales, boxes, point_coords
  )
- return roi_features.view(num_boxes, -1, output_size, output_size)
+ return roi_features.view(num_boxes, roi_features.shape[1], output_size, output_size)
 
  def _forward_mask_point(self, features, mask_coarse_logits, instances):
  """