Kyle Corbitt 299cd4cd01 Fix empty ScrollView warnings
Summary:Currently, an empty `<ScrollView />` on iOS always throws the warning "Sticky header index 0 was outside the range {0, 0}".

This is because the error-reporting code relies on the assumption that `stickyHeaderIndices` exists, and when it doesn't the error check thinks there's an index when there really isn't.

Note that this only changes error reporting and won't affect apps out of debug mode.

**Test plan**
I created a sample app and included an empty `<ScrollView />`. Without this change the "Sticky header..." warning was displayed on every run through. With this change implemented, the warning went away.
Closes https://github.com/facebook/react-native/pull/6417

Differential Revision: D3042178

Pulled By: nicklockwood

fb-gh-sync-id: 7afefd428a5fcb03867bcb69e46c46fe1ae9151e
shipit-source-id: 7afefd428a5fcb03867bcb69e46c46fe1ae9151e
2016-03-11 12:24:22 -08:00
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2016-03-11 12:24:22 -08:00