Crashes when fetching a project prevents it from being fetched again in the future
When a crash occurs while fetching a project, the directory of that project is kept as is, but the project is not added to the list of projects in the application. This means that a user would probably want to retry adding the project, but that will fail because the directory already exists, again crashing the application.
- make sure an error while fetching a project doesn't crash the application and cleans after itself
- a message should be shown when adding a project whose directory already exists.