Resolve /decide endpoint errors due to invalid token

[neilkakkar]

Changes

Fixes #4712

The problem was just a missing check for token being None, but I refactored this code a bit to ensure we don't have to remember to check this, if we use get_token anywhere in the future.

Checklist

• All querysets/queries filter by Organization, by Team, and by User
• Django backend tests
• Jest frontend tests
• Cypress end-to-end tests
• Migrations are safe to run at scale (e.g. PostHog Cloud) – present proof if not obvious
• Frontend/CSS is usable at 320px (iPhone SE) and decent at 360px (most phones)
• Breaking changes are backwards-compatible. Ensure old/new frontend requests work with new/old backends, and vice versa.

[macobo]

Nice, clean fix. Good job!

[neilkakkar]

Failing Cypress test seems flakey. Re-running again to see if it passes soon.

[buwilliams]

lgtm