shellDBus: Fix LaunchExtensionPreferences()

Commit 5dedc5d8ba removed "unused" functionality which was
still used by that method. Launch it via GAppInfo instead, which
still supports passing URIs.

https://bugzilla.gnome.org/show_bug.cgi?id=724813

js/ui/shellDBus.js

@@ -371,8 +371,10 @@ const GnomeShellExtensions = new Lang.Class({
     LaunchExtensionPrefs: function(uuid) {
         let appSys = Shell.AppSystem.get_default();
         let app = appSys.lookup_app('gnome-shell-extension-prefs.desktop');
-        app.launch(global.display.get_current_time_roundtrip(),
-                   ['extension:///' + uuid], -1, null);
+        let info = app.get_app_info();
+        let timestamp = global.display.get_current_time_roundtrip();
+        info.launch_uris(['extension:///' + uuid],
+                         global.create_app_launch_context(timestamp, -1));
     },
 
     ReloadExtension: function(uuid) {