Window.non blocking form fix

The non blocking form could only be opened once, after which subsequent attempts would generate a 'Show Non-Blocking Form called when form already active' error in the console, even though a 'nonBlockingFormClosed' event had been detected in JS.

WindowScriptinigInterface was checking for _editDialog on line 203 to test for an open form. Testing for  _nonBlockingFormActive instead produced the desired behaviour.