Ignore broken but excluded file during traversing

Ignore broken but excluded file during traversing

Walkdir's [`filter_entry()`][1] won't call the predicate if the entry
is essentially an `Err` from its underyling `IntoIter`. That means
Cargo hasn't had a chance to call `filter` on an entry that should be
excluded but eventually return an `Err` and cause the loop to stop.
For instance, a broken symlink which should bee excluded by `filter`
will generate an error since `filter` closure is not called with it.

The solution is calling `filter` if an error occurs with a path
(because it has yet been called with that path).
If it's exactly excluded, ignore the error.

[1]: https://github.com/BurntSushi/walkdir/blob/abf3a15887758e0af54ebca827c7b6f8b311cb45/src/lib.rs#L1042-L1058