When enabling an extension and installing its media, we work with a lock

to ensure that two processes aren't attempting to install media at the

same time. We then remove the lock file. This happens until the old

stored version in settings matches up with the current version of the

extension.
Where this falls apart is if an administrator copy/pastes a settings

dictionary from one server (say, a test server) into a disabled

extension's settings in the database editor, and then tries to enable

it. The versions will match up, but the extension won't be installed

yet, so we'll go through the locking phase. However, since the versions

match, we don't actually create a lock, and then we blow up trying to

remove it.
If the extension's data is not yet installed, its old version (if any)

is not to be trusted. Treat it like a fresh install.

I hit this a little while back when copying/pasting a settings dictionary

from one devserver to another. This fix prevented the problem from

happening.
Unit tests pass. They fail before this fix with the same error I hit before.