Jin fix imglayout

@maethu fixes:
...
Module zope.tales.expressions, line 217, in __call__
  Module Products.PageTemplates.Expressions, line 155, in _eval
  Module Products.PageTemplates.Expressions, line 117, in render
  Module ftw.contentpage.browser.textblock_view, line 21, in get_css_klass
TypeError: cannot concatenate 'str' and 'NoneType' objects