exa: apply patch to not panic on broken symlinks

Currently, exa fails when being executed in a git repository with
symlinks pointing to a non-existing location.

This can happen quite often with garbage-collected result links, or in
bazel repositories.

A fix was PR'ed in September at https://github.com/ogham/exa/pull/584,
but upstream seems to be not responding.

Let's apply this patch until there's a release containing the fixes.