Fix unclear IsRepositoryExist logic (#24374)

There was only one `IsRepositoryExist` function, it did: `has && isDir`

However it's not right, and it would cause 500 error when creating a new
repository if the dir exists.

Then, it was changed to `has || isDir`, it is still incorrect, it
affects the "adopt repo" logic.

To make the logic clear:

* IsRepositoryModelOrDirExist
* IsRepositoryModelExist

modules/repository/create.go

@@ -35,7 +35,7 @@ func CreateRepositoryByExample(ctx context.Context, doer, u *user_model.User, re
 		return err
 	}
 
-	has, err := repo_model.IsRepositoryExist(ctx, u, repo.Name)
+	has, err := repo_model.IsRepositoryModelExist(ctx, u, repo.Name)
 	if err != nil {
 		return fmt.Errorf("IsRepositoryExist: %w", err)
 	} else if has {