fix(useGetParticipants): ensure user is in the room before checking permissions

[Antreesy]

☑️ Resolves

• Patches a race condition UI <> signaling:
  • User leaves the call and conversation -> UI token already updated to new value (or '')
  • HPB sends the message with update.roomid = oldToken and update.users = [{ ...currentUser, callFlags: 0 }]
  • checkCurrentUserPermissions() -> conversation?... = undefined -> tries to fetch conversation with wrong token / no token

To test:

• Join and leave voice room

AI (if applicable)

• The content of this PR was partly or fully generated using AI

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

🏚️ Before	🏡 After
See console	---

🚧 Tasks

• FIXME - convert to issue? all _trigger() events currently passing only limited payload without token (although it's known)

🏁 Checklist

• 🌏 Tested with different browsers / clients:
  • Chromium (Chrome / Edge / Opera / Brave)
  • Firefox
  • Safari
  • Talk Desktop
  • Integrations with Files sidebar and other apps
  • Not risky to browser differences / client
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required

[Antreesy]

/backport to stable33