Method FatalConditionHandlerGuard

tests/catch.hpp:8039–8042

        FatalConditionHandler* m_handler;
    public:
        FatalConditionHandlerGuard(FatalConditionHandler* handler):
            m_handler(handler) {
            m_handler->engage();
        }
        ~FatalConditionHandlerGuard() {
            m_handler->disengage();
        }