macOS: on VM start, QEMU or other error messages disappear with the VM window

[conath]

With 2.0.26 there is a new feature, VMs are automatically closed when the guest shuts down. However the implementation does not consider errors when starting the VM. For example, adding an incorrect argument to QEMU section will result in a QEMU error alert when the VM is started. However now the VM window will instantly close again and take the error message with it.

To reproduce:

1. Create a new VM "from scratch".
2. Save it.
3. Open its configuration and open the QEMU tab.
4. Scroll down and enter into the "new..." field: -invalidargument
5. press Tab, then click on Save.
6. Start the VM

Expected:
7. The error message is presented and the VM window closes after the error is dismissed

Unwanted:
7. The error and the VM window close immediately after showing up.

[conath]

Just noticed another bug related to this. If you try to Quit UTM after encountering one or more of these disappearing errors, all of the windows will come back at once!

[conath]

Wow, it gets weirder. Pressing CMD-Q with a VM running and another VM previously closed, after a disappearing error, brings back the previously closed VM window (but it's non-interactive because the VM is not running).

EDIT: it seems like closing a VM's window no longer shuts it down. The window just hides.