Fix Syntax Error on Class Tag

@see http://issues.joomla.org/tracker/joomla-cms/5443
@see https://github.com/joomla/joomla-cms/issues/5443
Add Space After combobox Class

After Checking J3.0, J3.1's originally correct versions, there was a space between the combobox class and the custom class.
Merge pull request #5451 from bassmanpaul/patch-1

Fix Syntax Error on Class Tag