home: add xdg_data_home to session vars

hugin crashes if this is undefined

overlays/hugin/default.nix

@@ -9,7 +9,7 @@ final: prev: {
       fftw
       flann
       gettext
-      glew
+      glew-egl
       ilmbase
       lcms2
       lensfun
@@ -25,9 +25,7 @@ final: prev: {
       panotools
       sqlite
       vigra
-      (wxGTK31.override {
+      wxGTK30
-        withEGL = false;
-      })
       zlib
     ];
   });