Fix compat with latest RN master
Fix compat with latest RN master

The code in the Shape constructor assumes that `SvgTouchableMixin` contains only functions but [this](https://github.com/facebook/react-native/blob/master/Libraries/Components/Touchable/Touchable.js#L904) was added which breaks this assumption.

This simply makes sure whatever we assign is a function before calling `.bind`.
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