BUG: Lesions in background or surrounded by darker tissue could cause a divide by zero
BUG: Lesions in background or surrounded by darker tissue could cause a divide by zero

Fix this by checking lesion clusters for non-zero intensity. Also, for
very small clusters, dilate by 2 voxels instead of 1, to improve the
chance of finding suitable neighborhood voxels.

If lesions cannot be filled, they are skipped and a warning is printed

stnava/ANTs,stnava/ANTs,stnava/ANTs,stnava/ANTs,stnava/ANTs,stnava/ANTs,stnava/ANTs