fcitx5: fix svg loading

fcitx5 doesn't load svg's with highlight images

pkgs/tools/inputmethods/fcitx5/with-addons.nix

@@ -8,6 +8,7 @@
   libsForQt5,
   qt6Packages,
   fcitx5-gtk,
+  librsvg,
   addons ? [ ],
 }:
 
@@ -25,10 +26,15 @@ symlinkJoin {
   ]
   ++ addons;
 
+  buildInputs = [
+    librsvg
+  ];
+
   nativeBuildInputs = [ makeBinaryWrapper ];
 
   postBuild = ''
     wrapProgram $out/bin/fcitx5 \
+      --set GDK_PIXBUF_MODULE_FILE "$GDK_PIXBUF_MODULE_FILE" \
       --prefix FCITX_ADDON_DIRS : "$out/lib/fcitx5" \
       --suffix XDG_DATA_DIRS : "$out/share" \
       --suffix PATH : "$out/bin" \