Input activities for an If action are not stopped if if is unexecuted

Another issue relating to HPCC-22292 examples.  There is no code in CRoxieServerIfActionActivity::stop to stop the true and false dependencies.  That means that if the if action is not executed (because it is conditional, or referenced by an untriggered WHEN) then stop will not be called on the input actions.  If those input actions use a splitter that has been started then an error will be reported.