Description

Fixes case where user default model no longer exists

How Has This Been Tested?

• Create user Default
• Delete provider
• Verify chat not broken
• Re-create provider

Accepted Risk (provide if relevant)

N/A

Related Issue(s) (provide if relevant)

N/A

Mental Checklist:

• All of the automated tests pass
• All PR comments are addressed and marked resolved
• If there are migrations, they have been rebased to latest main
• If there are new dependencies, they are added to the requirements
• If there are new environment variables, they are added to all of the deployment methods
• If there are new APIs that don't require auth, they are added to PUBLIC_ENDPOINT_SPECS
• Docker images build and basic functionalities work
• Author has done a final read through of the PR right before merge

Backporting (check the box to trigger backport action)

Note: You have to check that the action passes, otherwise resolve the conflicts manually and tag the patches.

• This PR should be backported (make sure to check that the backport attempt succeeds)