Drop UI.rfb reference on all disconnects

We can be disconnected because of server reasons, not just because
someone clicked the disconnect button. Make sure we clean up the
reference and get a proper state in those cases as well.

app/ui.js

@@ -1048,8 +1048,6 @@ var UI = {
 
         UI.updateVisualState('disconnecting');
 
-        UI.rfb = undefined;
-
         // Don't display the connection settings until we're actually disconnected
     },
 
@@ -1102,6 +1100,8 @@ var UI = {
         // UI.disconnect() won't be used in those cases.
         UI.connected = false;
 
+        UI.rfb = undefined;
+
         if (!e.detail.clean) {
             UI.updateVisualState('disconnected');
             if (wasConnected) {