ZF2-406: Missing __isset / __unset in AbstractRowGateway

Description

isset() and unset() do not work correctly when accessing properties of an AbstractRowGateway object using object syntax. The __isset() and __unset() magic methods need to be implemented to make these features work as expected.

Comments

Pull request to resolve this issue: https://github.com/zendframework/zf2/pull/1911

Pull request has been accepted.