Prevent version update dialog from showing twice
Prevent version update dialog from showing twice

The problem with this is that launching the dialog a second time will
close the first dialog, therefore triggering a page reload.

rugk/threema-web,threema-ch/threema-web,rugk/threema-web,threema-ch/threema-web,threema-ch/threema-web,threema-ch/threema-web,threema-ch/threema-web,rugk/threema-web,rugk/threema-web