iter_frames raises AssertionError, when 00,20,40 folders are missing.

[aschle]

When folders like 00, 20, and 40 are missing (due to maintenance or whatever else), a AssertionError is raised.
Maybe, that's because it is somehow searching for the next directory until it reaches the end of the repositories folder structure.
I don't knot what exactly is happening, but it somehow iterates all the folders, until it reaches the end.