purge: prevent a silly crash with --confirm --files
if --files is passed, there was no directory to checks and `msg` was undefined.
This is now fixed and tested.
= Mercurial XXX =
== New Features ==
== Default Format Change ==
These changes affect newly created repositories (or new clones) done with
Mercurial XXX.
== New Experimental Features ==
== Bug Fixes ==
== Backwards Compatibility Changes ==
== Internal API Changes ==
== Miscellaneous ==