'Export as archive' deletes original save file

Steps to reproduce:

1. Create new project
2. Save project
3. Click 'Export as archive' from the menu
4. Save it in the same directory in which you saved the project file
5. Notice that the previous save was deleted

While exporting, temporary save file is created and then deleted when no longer needed. tmp_name is generated with project.name, which in turn is generated from previous save uri. So the temporary save-file will have the same name as the previous save