Don't stop or warn if the edited file was deleted on disk
If an open file with unsaved changes was deleted on disk, Okular currently warns the user about it (in master) or prevents them from saving it (in 23.04). But in both cases this is unnecessary; if the open file was deleted on disk when the user tries to save changes, Okular can simply save to its file path and re-create it, with no risk of data loss or stomping on anyone else's work. So it should do that.