fix linearlite loading if issue url is opened directly with no synced issue database

[alsuren]

I was trying to debug something unrelated and found that the IssuePage was getting into a bad state if you browsed directly to it in an incognito tab without visiting the main page first.

The fix is reasonably trivial: delay all rendering queries until the initial db dump in synced, like how the rest of the example works.

I also fixed the "not found" rendering. I don't think that useLiveQuery(liveIssue).rows[0] can ever be null: it will always be Item | undefined (typescript types it as Item unless you turn on noUncheckedIndexedAccess).

steps to test

• check that navigating to issue with no synced issue database works
  • open http://localhost:5173/ and click on an issue to get issue url (it will look like http://localhost:5173/issue/d8af89e7-d1cf-4488-8b1b-424f120d0aa6)
  • open a new incognito window (⌘⇧N) and go to that url
    • in main, you would get Loading... forever (it would fix itself if you refresh the page)
    • on this branch, it should load correctly
• check that navigating to a nonexistent issue tells you "not found"
  • open an issue that doesn't exist (e.g. http://localhost:5173/issue/00000000-0000-0000-0000-000000000000)
    • on main, you would get Loading...
    • on this branch, you should get Issue not found

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