[BUGFIX] AOP works with __clone call on parent objects
If, for example, you extend an entity which implements __clone
the AOP Framework breaks with an warning in development mode,
that it cannot access Flow_Aop_Proxy_targetMethodsAndGroupedAdvices.
Solution is to check if the private
Flow_Aop_Proxy_targetMethodsAndGroupedAdvices property is
accessible and otherwise skipping the Advice call.
Releases: master, 2.3, 2.2, 2.1