Make onEndReachedThreshold=null match default value if prop not provided
Make onEndReachedThreshold=null match default value if prop not provided

Summary:
This change makes the behavior of providing a null value to onEndReachedThreshold match the behavior of not providing the prop at all.

## Changelog:

[General] [Changed] - Adjusted VirtualizedList's onEndReachedThreshold default value when null is provided

Reviewed By: olegbl

Differential Revision: D22870445

fbshipit-source-id: 29cbf0550702244007689759846ae0356f06b48d

facebook/react-native,myntra/react-native,hoangpham95/react-native,hoangpham95/react-native,hoangpham95/react-native,janicduplessis/react-native,javache/react-native,arthuralee/react-native,janicduplessis/react-native,pandiaraj44/react-native,pandiaraj44/react-native,janicduplessis/react-native,myntra/react-native,janicduplessis/react-native,javache/react-native,hoangpham95/react-native,myntra/react-native,hoangpham95/react-native,facebook/react-native,pandiaraj44/react-native,javache/react-native,javache/react-native,pandiaraj44/react-native,myntra/react-native,myntra/react-native,facebook/react-native,myntra/react-native,arthuralee/react-native,arthuralee/react-native,facebook/react-native,hoangpham95/react-native,pandiaraj44/react-native,facebook/react-native,myntra/react-native,javache/react-native,javache/react-native,javache/react-native,hoangpham95/react-native,pandiaraj44/react-native,pandiaraj44/react-native,facebook/react-native,javache/react-native,hoangpham95/react-native,facebook/react-native,janicduplessis/react-native,arthuralee/react-native,arthuralee/react-native,pandiaraj44/react-native,janicduplessis/react-native,javache/react-native,myntra/react-native,facebook/react-native,facebook/react-native,myntra/react-native,janicduplessis/react-native,janicduplessis/react-native