The crash happens because of trying to create subdir "autosave" in the project directory, which is not existing anymore.

The fix
a) avoids creating the subdir, if the project dir is not existing
b) catches any exception in autosave, so autosave itself never causes a crash by an unhandled exception

2nd path is:
Open BA - Open Project - cancel - save project - crash

The crash fix is to always create a new project (done in method ProjectManager::newProject())

Furthermore NewProjectDialog distinguishes now between "create" and "save", since  otherwise it would look ugly on the UI. Imagine these steps:

Open BA, edit something, click "create new project". Now first a dialog for saving is shown, then a dialog for creating. Without the done changes, two dialogs with title "Create project" would show up.

This resolves Redmine #2498