User credentials list fails to load when associated tools are missing

[itisAliRH]

Describe the bug
The list of provided credentials in user preferences does not load if any of the associated tools cannot be found or have been deleted from the instance.

Galaxy Version and/or server at which you observed the bug
Galaxy Version: 26.0.dev0
Commit: cf09b27

To Reproduce
Steps to reproduce the behavior:

1. Add a tool with credentials to your instance
2. Provide credentials for it
3. Remove the tool from the instance
4. See error

Expected behavior
List the available credentials, including those for tools that have been removed or are not found.