`pixel` variable can be undefined

[bhashemian]

Describe the bug

MONAI/monai/apps/pathology/transforms/post/array.py

Line 461 in d0d720d

sequence.append(pixel)

If none of the if/elif conditions are satisfied, pixel is undefined here.

[KumoLiu]

I created a PR to add FillHoles before generate_instance_contour, which may prevent the issue when instances contain holes.

[bhashemian]

Thanks @KumoLiu! That helps in this pipeline so it is not a blocker anymore but we should consider the edge cases to work with this transform. Can you see if you can skip that particular contour or that image instead of raising error (and maybe just give a warning to the user)? Thanks