File Permission Error Handling

[adeutscher]

The Updog listing 403's if given a directory with a symbolic link to an inaccessible file.

To reproduce:

1. Create a directory with a dead symbolic link on account of the destination being unreachable. I discovered this browsing my /etc directory, which had a symlink to something walled off to my user in /boot.
2. View directory in Updog.

Expected behavior is that only the affected path should be be affected, not the parent directory with the link.

[adeutscher]

The cause of the issue is that the is_dir/is_file methods of DirEntry throw PermissionErrors when used on a walled-off symbolic link.