Unsaved new documents created in a second window appear lost if the window is closed

### What Happened?

Created a new document and opened it in a new window. Edited the document. Closed the window. The window closed without warning. The autosave feature was off.

The document was in fact saved in `~/.local/shared/io.elementary.code/unsaved` but was not restored when the app was closed and restarted as it was not open in the first window. There was no way to restore it through the apps UI unless you knew where it was.

### Steps to Reproduce

1. Turn off autosave
2. Create a new document and then open it in a new window.
3. Alternatively, open a new window and create a new document in it.
4. Add some text
5. Close the window
6. The window closed without any warning
7. Close the app and restart it
8. The new document is not restored
9.

### Expected Behavior

Either throw a warning dialog when a window is closed with an unsaved new document or restore all unsaved new documents into the first window on restarting the app (subject to privacy settings).

### OS Version

8.x (Circe)

### Session Type

Classic Session (X11, This is the default)

### Software Version

Latest release (I have run all updates)

### Log Output

_No response_

### Hardware Info

_No response_