Fix torch.chunk int32 overflow (#5191)
Fix torch.chunk int32 overflow (#5191)

* Update fcn_mask_head.py

* Update fcn_mask_head.py

* Update fcn_mask_head.py

* Resolve format issues

Co-authored-by: Wenwei Zhang <fabb68f4fed156ebae3036303d1cedae0bf2feeb@users.noreply.github.com>
open-mmlab/mmdetection,open-mmlab/mmdetection