Bug: when deleting a folder that contains a file we can't delete, we get an uninformative message

To reproduce:

1. Create folder /path_to_my/folder
2. Create nested_folder /path_to_my/folder/nested_folder
3. Create a file inside nested_folder /path_to_my_folder/folder/nested_folder/file.txt
4. Change the permissions of nested_folder to be read only.
5. Start diskonaut and give it /path_to_my as its path (diskonaut /path_to_my).
6. Try to delete folder.
7. See that we get an uninformative error message and are unsure what happened.

In this scenario, the message should read something like "Permission denied deleting /path_to_my/folder/nested_folder".