window_zoom_persist is partially broken

In bsp mode, if there are less than 4 windows equally divided on the screen, with `window_zoom_persist` set to `on`, creating a new window is behaving exactly as in [#1481](https://github.com/koekeishiya/yabai/issues/1481#issuecomment-1279765707).

Actual behavior:

1. bsp mode
2. Open 2 windows
3. fullscreen-zoom one
4. Create a new window
5. See that zoomed-in window is zoomed-out to a half of the screen

Expected behavior:

`5.` doesn't happen and zoomed-in window stays intact

Note: this doesn't happen when there are 4 windows (2 | 2, 2 - 2) on the screen or more, or there are 3 windows, and the zoomed-in window is one of the smallest.

No file or test is named in the issue. First reproduce the five-step bsp scenario with window_zoom_persist enabled, then trace the fullscreen-zoom state while creating the third window. Done means the zoomed window remains intact for the described two-window case without regressing the documented three- and four-window behavior.

Written by the indexing model from the issue text.