fix(messagesStore): fix posting new messages in the thread

[Antreesy]

☑️ Resolves

• Fixups extracted from thread blocks PR:
  • fix posting new messages in the thread
    • when posting in thread, we don't always have first message in messagesStore, but in threadInfo.first
  • set 0 timeout for non-polling requests
    • when getting old/new messages, and we know it's not long polling, we shouldn't make server hold the request
  • block route navigation from '#' items
    • upstream bug with <a href='#'> on some components. for now enough to avoid duplicated navigation
  • adjust temporary method to get thread-only blocks
    • with lastMessage always as chatBlocks[0], we should ignore it
  • focus context message if known already
    • when switch between two already loaded chats, contextMessage should be focused

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

No visual changes

🏁 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