rust-status: don't dispatch unknown file when traversing if not listing unknowns...
rust-status: don't dispatch unknown file when traversing if not listing unknowns
This usually isn't a (functional) problem since we ignore the unknown files
anyway, but when specifically using `hg purge`, unknown files were iterated over
regardless of the option being true.
This is both more correct and more efficient.
Differential Revision:
https://phab.mercurial-scm.org/D8517
