App crashes on macOS when secrets for an account are missing

As reported by a user:

The app crashes on macOS. The issue is as follows (and in theory can hit us on every OS):

• We fail to load credentials for an account or old library.
• For some reason, this fails.
• We now try to create a problem report. In the appropriate code where we try to load an account by its ID, we don't find it (because probably we try to load credentials for a library), however, we access the nullptr object unconditionally.