filezilla: add wrapper to set necessary FZ_DATADIR

Filezilla fails to start currently, with the following message being
shown in a lone dialog before the program exits:

> Could not find the resource files for FileZilla, closing FileZilla.
> You can set the data directory of FileZilla using the '--datadir
> <custompath>' commandline option or by setting the FZ_DATADIR
> environment variable.

This commit adds a wrapper for the filezilla binary to set the
environment variable to the package root, which fixes the issue.

pkgs/applications/networking/ftp/filezilla/default.nix

@@ -1,5 +1,7 @@
 { stdenv, fetchurl, dbus, gnutls, wxGTK30, libidn, tinyxml, gettext
-, pkgconfig, xdg_utils, gtk2, sqlite, pugixml, libfilezilla, nettle }:
+, pkgconfig, xdg_utils, gtk2, sqlite, pugixml, libfilezilla, nettle
+, makeWrapper
+}:
 
 let version = "3.31.0"; in
 stdenv.mkDerivation {
@@ -17,7 +19,11 @@ stdenv.mkDerivation {
   nativeBuildInputs = [ pkgconfig ];
   buildInputs = [
     dbus gnutls wxGTK30 libidn tinyxml gettext xdg_utils gtk2 sqlite
-    pugixml libfilezilla nettle ];
+    pugixml libfilezilla nettle makeWrapper ];
+
+  postInstall = ''
+    wrapProgram $out/bin/filezilla --set FZ_DATADIR $out
+  '';
 
   meta = with stdenv.lib; {
     homepage = https://filezilla-project.org/;