ZF-6371: Cannot set editor element height to empty string

Description

 Message: Invalid height provided; must be integer or CSS measurement
Stack trace:

#0 C:\...\library\Zend\ZendFramework-1.7.7\library\Zend\Form\Element.php(328): Zend_Dojo_Form_Element_Editor->setHeight('')

but

Dojo says:

{quote}Set height to fix the editor at a specific height, with scrolling. By default, this is 300px. If you want to have the editor always resize to accommodate the content, use AlwaysShowToolbar plugin and set height=""{quote}

Comments

Attached patch + tests.

I've reviewed the patch and confirm it operates as intended. Recommend committing to trunk and merging to release branch.