Fix #1774: refresh folder list after disabling Unread Only

[Keegil]

Bug fix — Message list stays empty after disabling Unread Only when no unread messages exist in the folder.

Problem

When a folder contained no unread messages, enabling Unread Only produced an empty list (expected). Disabling Unread Only afterwards left the list empty instead of repopulating it with all messages. The issue only occurred in this specific state (empty filtered result set, no local index). Issue #1774.

Fix

• Force a filter reapplication even when the current filtered result set is empty
• Repopulate the folder message list after Unread Only is turned off without requiring a local index to be present

Testing

• Regression test added for the filter-refresh code path
• npm run lint passes (existing repo-wide warnings only)
• npx ng build runbox7 succeeds

Fixes #1774