A user hit an issue on an iPhone 5s. Device transfer would fail because
their app group was missing the ProfileAvatars directory.
This directory is lazily created as a post-launch job at background QoS.
It's not too big of a deal and it'll be created on demand if necessary.
The 5s was probably CPU constrained enough to never have a chance to run
any background jobs.
The fix is to just have our recursive filesystem traversal ignore any
unknown directory errors. This is only used in a couple places and the
behavior makes sense in each place.
