fix(useGetMessages): better handle race condition for chat context

[Antreesy]

☑️ Resolves

• Regression from #ebf5e16dcbfd30ac96d057de58d0c568ed97bc28
• Exposed by fix(useGetMessages): always start message polling #16178

handleStartGettingMessagesPreconditions can be called, when:

• vue-router is ready and all conditions met
• wacher is triggered and all conditions met

At the time of commiting (21.07.2025) watcher and router were triggered in different order, so everything was working fine. Now second called function cancels server request, which hasn't even started yet, causing it to not appear in the Network tab (yet 'await' for getMessagesContext considered fulfilled)

Solution: early return.

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

🏚️ Before	🏡 After

🏁 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]

Can we merge them together

Tried, no. if await for router.isReady(), it will replace current route -> replace current token -> trigger watcher again

But also duplicating of if was done before we migrate useGetToken to new logic. so described thing would always happen now, and we don't need that

[Antreesy]

/backport to stable32