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