gui: Overwrite existing files.
gui: Overwrite existing files.

As the user already consents to that in the save dialog.

Fixes #408.

schulmar/apitrace,apitrace/apitrace,apitrace/apitrace,trtt/apitrace,schulmar/apitrace,schulmar/apitrace,trtt/apitrace,trtt/apitrace,schulmar/apitrace,apitrace/apitrace,schulmar/apitrace,trtt/apitrace,apitrace/apitrace,trtt/apitrace