xcur2png: fix gcc-14 build

Without the change the build against `gcc-14` fails as:

    $ nix build --impure --expr 'with import ./. {}; xcur2png.override { stdenv = gcc14Stdenv; }'
    ...
    xcur2png.c: In function 'saveConfAndPNGs':
    xcur2png.c:690:10: error: type defaults to 'int' in declaration of 'dry_run' [-Wimplicit-int-Wimplicit-int]
      690 |   extern dry_run;
          |          ^~~~~~~

pkgs/tools/graphics/xcur2png/default.nix

@@ -28,6 +28,13 @@ stdenv.mkDerivation rec {
       url = "https://github.com/eworm-de/xcur2png/commit/aa035462d950fab35d322cb87fd2f0d702251e82.patch";
       hash = "sha256-hlmJ/bcDSl1ADs0jp+JrAgAaMzielUSRVPad+plnSZg=";
     })
+
+    # fix gcc-14-build:
+    #   https://github.com/eworm-de/xcur2png/pull/4
+    (fetchpatch {
+      url = "https://github.com/eworm-de/xcur2png/commit/6fb03957aba8aebc3dc98a479fff9cddf85b9e7b.patch";
+      hash = "sha256-COG4/MKfBAwQU5FqZeqEE4jJT4XII7AQ6ayRSuFcUmY=";
+    })
   ];
 
   nativeBuildInputs = [