[NEXUS-5766] Walker should not give up if a collection was removed while walking it

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
Merge pull request #47 from sonatype/NEXUS-5766-snapshot-remover-ignore-inf

REVIEW: [NEXUS-5766] Walker should not give up if a collection was removed while walking it