Resolves: rhbz#1285364 urls cannot be opened under wayland

because we're setting DISPLAY always, and under wayland that resolves to
"wayland", not the original ":0" so the gtk2 gvfs-open eventually called open
xdg-open cannot open the correct display

(cherry picked from commit 3bb7557d)

Change-Id: I246120f2430b92cd2d3e5003445aa4c9da4f6a68
Reviewed-on: https://gerrit.libreoffice.org/20721Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
(cherry picked from commit bd05312d)

vcl/unx/gtk/app/gtkdata.cxx

@@ -712,6 +712,7 @@ void GtkData::Init()
         exit(0);
     }
 
+#if !GTK_CHECK_VERSION(3,0,0)
     /*
      * if a -display switch was used, we need
      * to set the environment accoringly since
@@ -722,6 +723,7 @@ void GtkData::Init()
     const gchar *name = gdk_display_get_name( pGdkDisp );
     OUString envValue(name, strlen(name), aEnc);
     osl_setEnvironment(envVar.pData, envValue.pData);
+#endif
 
     GtkSalDisplay *pDisplay = new GtkSalDisplay( pGdkDisp );
     SetDisplay( pDisplay );