Activityid is replaced when create event from another module

When you add new event from another module the return_id in the REQUEST
replace the activityid that was saved in a varible called $return_id to after
execute a header location to return to this record.

This produce a problem when the event has to send a invitation, because first call
to $mail_contents = getRequestData($return_id); and getRequestData expect an activityid