Merge pull request #378 from csmith/master

Fix silly NPE in InviteLabel.

ui_swing/src/com/dmdirc/addons/ui_swing/components/statusbar/InviteLabel.java

         if (event.getWindow().isPresent()) {
             activeConnection = event.getWindow().get().getContainer().getConnection();
         } else {
-            activeConnection = null;
+            activeConnection = Optional.empty();
         }
         update();
     }