Fix BC #6008 for relation detection by ensuring method exists
Fix BC #6008 for relation detection by ensuring method exists

Makes sure the method exists and is callable instead of just callable

greg0ire/SonataAdminBundle,jordisala1991/SonataAdminBundle,sonata-project/SonataAdminBundle,osavchenko/SonataAdminBundle,osavchenko/SonataAdminBundle,greg0ire/SonataAdminBundle,peter-gribanov/SonataAdminBundle,peter-gribanov/SonataAdminBundle,Armstrong1992/SonataAdminBundle,sonata-project/SonataAdminBundle,jordisala1991/SonataAdminBundle,osavchenko/SonataAdminBundle,greg0ire/SonataAdminBundle,osavchenko/SonataAdminBundle,peter-gribanov/SonataAdminBundle,greg0ire/SonataAdminBundle,osavchenko/SonataAdminBundle,Armstrong1992/SonataAdminBundle,peter-gribanov/SonataAdminBundle,jordisala1991/SonataAdminBundle,jordisala1991/SonataAdminBundle