Window without on_close handler can't be closed with the window decoration

[freakboy3742]

Describe the bug

If a window is defined without an on_close handler, The close button (X or red button on the window frame) cannot be used to close the window

Steps to reproduce

1. Run the windows example
2. Click on the "create windows" button
3. Try to close the window with "no on_close handler"

The window should, but will not close. There are no errors or log messages.

Programmatically invoking window.close() does work.

Expected behavior

The window should close.

Screenshots

No response

Environment

• Operating System: Windows, macOS, Linux
• Python version: All
• Software versions:
  • Toga: 0.3.1

Logs

No response

Additional context

As a workaround, adding on_close=lambda w: True to the window will allow it to close.

This is likely caused by 0d9d43a from #1833.

[mhsmith]

Overlaps with #1714.

[freakboy3742]

There may be some conceptual overlap, but this is a specific regression in the on_close handler; this functionality worked in 0.3.0. #1714 is new (albeit definitely required) functionality.