Closing event edit window before permission dialog crashes

## Prerequisites
- [x] I have searched open and closed issues for duplicates.

## Describe the bug
I have location permissions turned off for Calendar. When I open the event dialog, it pops up a permission dialog. If I close the event dialog before the permission, then when I close the permission one, the whole app crashes.

### To Reproduce
Steps to reproduce the behavior:
1. Turn off location permission for Calendar
2. Create a new event. Both dialogs should appear.
3. Click the cancel button on the **event** dialog (NOT the permission dialog). The permission dialog should remain open.
4. Click the cancel button on the permission dialog.
5. Calendar crashes.

### Expected behavior

The app should stay up. If there's a way to close the dialog when the event dialog that caused it is closed, that would be a nice way to do it. Or if there's a way to make the permission dialog modal to the event dialog, that would ensure that we can't close the event dialog erroneously.

### Logs
Here's the relevant line. It's only one assertion error. Before this is other irrelevant info.
```
(io.elementary.calendar:11943): GLib-GObject-CRITICAL **: 21:35:22.315: g_value_set_object: assertion 'G_IS_OBJECT (v_object)' failed
Application exited
```

## Platform Information

- [x] I'm using the latest version from git that I've manually compiled
- [ ] I'm using the latest released stable version

## Additional context

It's possible the modality issue could be an issue with the OS that presents it. I'm open to suggestions here.

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