MNTOR-2973: null currentFxAProfile fix

[mansaj]

References:

Jira: MNTOR-2973

Description

currentFxAProfile[key] is throwing error when currentFxAProfile is null, causing fxa webhooks to fail with 500s

Screenshot (if applicable)

Not applicable.

How to test

Checklist (Definition of Done)

• Localization strings (if needed) have been added.
• Commits in this PR are minimal and have descriptive commit messages.
• I've added or updated the relevant sections in readme and/or code comments
• I've added a unit test to test for potential regressions of this bug.
• Product Owner accepted the User Story (demo of functionality completed) or waived the privilege.
• All acceptance criteria are met.
• Jira ticket has been updated (if needed) to match changes made during the development process.
• Jira ticket has been updated (if needed) with suggestions for QA when this PR is deployed to stage.