The parameter to `ModalDialog.close(timestamp)` is optional. But when
invoked via the network dialog's Cancel button it was receiving an
implicit parameter value that's definitely not a timestamp:
```
[0x560f18af0c50 StButton.modal-dialog-linked-button:first-child hover ("Cancel")]
```
And as of today (or gjs >= 1.67.3) that's reported as an error:
```
JS ERROR: Error: Argument timestamp: value is out of range for uint32
popModal@resource:///org/gnome/shell/ui/main.js:638:12
popModal@resource:///org/gnome/shell/ui/modalDialog.js:206:14
close@resource:///org/gnome/shell/ui/modalDialog.js:179:14
```
and so you can't Cancel the dialog anymore.
Make sure `ModalDialog.close()` receives an `undefined` timestamp it
knows how to handle.
Fixes: https://bugs.launchpad.net/bugs/1918666
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1757>
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