loader: Handle missing revision tree entry
It exist some rare cases when a tree entry is missing for a bazaar revision. In that case, skip its processing and continue to next entry.
This fixes the loading of those repositories (reported in SWH-LOADER-BZR-71):
- https://code.launchpad.net/~ubuntu-branches/ubuntu/quantal/pspp/quantal
- https://code.launchpad.net/~ubuntu-branches/debian/wheezy/pspp/wheezy
- https://code.launchpad.net/~ubuntu-branches/ubuntu/precise/pspp/precise
- https://code.launchpad.net/~ubuntu-branches/debian/sid/pspp/sid
Unfortunately, I do not know how to create a sample repository for that edge case to be used in tests.