Summary:
If FlatList is passed non-array data it will return `undefined` as the result of `getItemCount()` to VirtualizedList. This change makes it return `0` instead, to signify there are no valid items to attempt to accces.
There are a set of invariants on properties passed to FlatList, to curb incorrect types at runtime, but there is existing code which runs into the condition.
Changelog:
[Internal][Fixed] - Guard FlatList getItemCount() against non-array data
Reviewed By: javache
Differential Revision: D38198351
fbshipit-source-id: 9efd0df7eeeba17078e2c838d470c4b0d621b9a0