Update editor.php

When a bad coded or outdated (i.e.) non-compatible plugin is installed you cannot open the editor and an error is shown "Call to undefined method stdClass::onDisplay() Error". Only 2 fields are visible "Name and Alias". I posted the entire issue on https://groups.google.com/forum/#!searchin/joomla-dev-cms/$2Flibraries$2Fcms$2Feditor$2Feditor.php/joomla-dev-cms/-2EPgbbNn78/7LKB3_5Ah8IJ and will post also a Tracker item shortly. 

The code change checks to see if the class method named “onDisplay” exists before attempting to use it but will pass without throwing the error 

Leo Lammerink
MD GWS-Desk.com
Merge pull request #3166 from gwsdesk/patch-1

Update editor.php