inline edit occasionally fails

occasionally, inline edit will fail building the form for lack of classname:
https://github.com/civicrm/civicrm-core/blob/master/CRM/Core/Page/AJAX.php#L55

rather than fail in the ajax function and trigger a fatal error to the user, we should check for the existence of a class name when the inline edit block is clicked and block editing if it either doesn't exist or was not passed correctly.

as to why it may not have been passed – I speculate it's most likely a browser issue. the values are not retrieved correctly as set in the data-edit-params element and thus not passed to the function.