When the webui auth session expires (e.g., after a server restart),
api() returns undefined after redirecting to /login. Previously,
loadSession() and _ensureMessagesLoaded() would dereference the
undefined response and throw, surfacing a confusing 'Failed to load
session' toast while the browser was already navigating away.
Add guards after api() calls that may trigger 401 redirects:
- loadSession(): bail early if data is undefined
- _ensureMessagesLoaded(): return silently if data is missing
- _loadOlderMessages(): return silently if data is missing
This prevents the stuck loading state and unnecessary error toasts
when the user is already being redirected to re-authenticate.
Fixes#1391 (reported as 'Failed to load session' after restart)
22fce2fda1
