Allow user level scans

[milosdjakonovic]

At present, when PHP Antimalware Scanner comes to unreadable directory unrecoverable error happens and all subsequent actions are gone. It's enough that there's a single unreadable dir (probably the same is true for file) and the whole scan is error-terminated.

In my opinion this isn't the best design; also, a non-root scans are frequently affected by this.

Solution: allow scanner to skip unreadable directories (PR is on the way).

[marcocesarato]

Thanks for your pull request, very appreciated. Merged.