[FIXUP] dogtail tests: Refactor the openProject helper to handle unsaved changes better
project: Remove some nonsensical code from loadProject

- Useless code since it wouldn't ever be run after return statements
- Empty return statements that are not actually needed as they are at the end
mainwindow: Pass exception messages correctly when errors occur while saving

This was a regression introduced by commit 267dd141
dogtail tests: Verify more carefully that backups load correctly/completely

Also do general refactoring to make the code more robust and easier to follow