Handle ErrorKind::Interruped in walk

[wezm]

While scanning a hierarchy dust reported an ErrorKind::Interruped error.

It appears this originates in:

dust/src/dir_walker.rs

Line 240 in dbd18f9

editable_error.unknown_error.insert(failed.to_string());

As per the docs I think this error should be detected and the read_dir tried again.

There's also some guidance in the Read trait docs:

An error of the ErrorKind::Interrupted kind is non-fatal and the read operation should be retried if there is nothing else to do.