Frontend Exceptions should be handled appropriately

[mattheworris]

As a developer, I do not want the frontend to throw exceptions and disrupt the user experience.

Acceptance Criteria

• [ ] frontend/src/content/PostList.tsx:41 throws exceptions that result.posts is not iterable error This error has been masked for debugging, but needs a deeper solve.
• [ ] frontend/src/chrome/UserAvatar.tsx:28 throws errors when msaId is undefined. This error has been masked for debugging, but the root-cause of msaId being undefined should be solved, or correctly handled.

[claireolmstead]

No longer seeing these bugs.