refind: Fix possible NULL dereference

This was observed with U-Boot.

See the upstream change.

 - https://sourceforge.net/p/refind/code/merge-requests/45/

pkgs/tools/bootloaders/refind/default.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchurl, gnu-efi, nixosTests }:
+{ lib, stdenv, fetchurl, fetchpatch, gnu-efi, nixosTests }:
 
 let
   archids = {
@@ -24,6 +24,13 @@ stdenv.mkDerivation rec {
   patches = [
     # Removes hardcoded toolchain for aarch64, allowing successful aarch64 builds.
     ./0001-toolchain.patch
+
+    # Fixes issue with null dereference in ReadHiddenTags
+    # Upstream: https://sourceforge.net/p/refind/code/merge-requests/45/
+    (fetchpatch {
+      url = "https://github.com/samueldr/rEFInd/commit/29cd79dedabf84d5ddfe686f5692278cae6cc4d6.patch";
+      sha256 = "sha256-/jAmOwvMmFWazyukN+ru1tQDiIBtgGk/e/pczsl1Xc8=";
+    })
   ];
 
   buildInputs = [ gnu-efi ];