Calendar: Add Event - dialog squished to side of screen

[castaway]

Describe the bug If we click on "Add event" while the calendar is still loading the existing calendars/events, the dialog box for the new event does not display in the screen centre, but oddly off the side of the window.

To Reproduce Steps to reproduce the behavior:

1. Login to an account with several calendars/events
2. Quickly click on 'Add event' before loading has finished
3. Note odd position of dialog box (only partly there, unusable)

Expected behavior Dialog box appears mid screen as usual (or we cant use button until calendar loaded)

Screenshots If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Linux, macOS
• Browser Firefox
• Version

[runboxdave]

It looks like this.

[shadowbas]

I get a very small dialog: