Fix residual empty directory when clone fails.

- Currently an empty directory will be created when trying
to clone non-existant remote repo.
- This commit adds an action to delete the repo directory
if an exception occurs while cloning.

Author: YuPeiHenry

src/GitHub.App/Services/RepositoryCloneService.cs

@@ -223,6 +223,7 @@ public async Task CloneRepository(
             }
             catch (Exception ex)
             {
+                operatingSystem.Directory.DeleteDirectory(repositoryPath);
                 log.Error(ex, "Could not clone {CloneUrl} to {Path}", cloneUrl, repositoryPath);
                 throw;
             }