Issues caused by disabling 'Close window with last tab'

Steps to reproduce the issue:

1. Create a new Orion profile
2. Go to Settings -> Tabs -> toggle off 'Close window with last tab'
3. Open a new private browsing window
4. Close the tab that opens with the window
5. Orion now has 0 tabs open in that window
6. You can continue pressing ⌘+Wto "close" the 0th tab
7. Attempting to left click on any items on your Orion start page will not result in anything
8. Right clicking the start page items and selecting 'Open in new tab' correctly opens them in a new tab

Video of the issue:

In the video, I first showcase how Orion behaves with the setting enabled. Upon disabling it, I highlight the broken behavior. Some of the issues are also present in non-private tabs as well, making 0 open tabs a very common sight:

Expected behavior:
It shouldn't be possible to break the window by closing tabs. If the result is 0 open tabs, Orion should default to opening a new tab according to the 'New tabs open with' setting in General settings.

Orion and macOS versions:

Version 0.99.132.1-rc (WebKit 621.1.2.111.4)

Sequoia (15)