[TxMt] TextMate::UI.request_item no longer working?

[Stefan Daschek]

Today I noticed that a bundle command using TextMate::UI.request_item is 
no longer working: Instead of opening a dialog window it only gives a 
warning:

tm_dialog (async_close): Window '(null)' doesn't exist

Simple command to reproduce:

```
#!/usr/bin/env ruby18 -wKU
require "#{ENV["TM_SUPPORT_PATH"]}/lib/ui"
TextMate::UI.request_item(:items => %w(foo bar baz), :title => 'Title')
```

Known bug?