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 ogham/exa#584,
but upstream seems to be not responding.

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

pkgs/tools/misc/exa/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchFromGitHub, rustPlatform, cmake, perl, pkgconfig, zlib
+{ stdenv, fetchFromGitHub, fetchpatch, rustPlatform, cmake, perl, pkgconfig, zlib
 , darwin, libiconv, installShellFiles
 }:
 
@@ -17,6 +17,15 @@ buildRustPackage rec {
     sha256 = "14qlm9zb9v22hxbbi833xaq2b7qsxnmh15s317200vz5f1305hhw";
   };
 
+  patches = [
+    (fetchpatch {
+      # https://github.com/ogham/exa/pull/584
+      name = "fix-panic-on-broken-symlink-in-git-repository.patch";
+      url = "https://github.com/ogham/exa/pull/584/commits/a7a8e99cf3a15992afb2383435da0231917ffb54.patch";
+      sha256 = "0n5q483sz300jkp0sbb350hdinmkw7s6bmigdyr6ypz3fvygd9hx";
+    })
+  ];
+
   nativeBuildInputs = [ cmake pkgconfig perl installShellFiles ];
   buildInputs = [ zlib ]
   ++ stdenv.lib.optionals stdenv.isDarwin [