If isOpen isn't set, don't respect its value when props change.
If isOpen isn't set, don't respect its value when props change.

This fixes and issue where updating other props of the menu (in particular, the
children) would cause the view to see that its own isOpen state !== undefined
and it would then close itself.

Kureev/react-native-side-menu,Kureev/react-native-side-menu,react-native-fellowship/react-native-side-menu