Fixing RN Picker

Summary:
Changelog: [Internal]

Fixing a red screen on the RN picker.
Looks like the picker gets confused when  for unknown reasons a native value is undefined. In that case we stick to the JS value as it is specified in the comment.
https://fb.workplace.com/groups/rn.support/permalink/2997783536936908/

NOTE : Native fix was landed, this add an extra layer on the JS side

Reviewed By: mmmulani

Differential Revision: D18443005

fbshipit-source-id: 9511ac90f2d9e6186c6c0de3b673cc535cdb9fa6

Libraries/Components/Picker/PickerIOS.ios.js

@@ -115,7 +115,11 @@ class PickerIOS extends React.Component<Props, State> {
     // This is necessary in case native updates the picker and JS decides
     // that the update should be ignored and we should stick with the value
     // that we have in JS.
-    if (this._picker && this._lastNativeValue !== this.state.selectedIndex) {
+    if (
+      this._picker &&
+      this._lastNativeValue !== undefined &&
+      this._lastNativeValue !== this.state.selectedIndex
+    ) {
       PickerCommands.setNativeSelectedIndex(
         this._picker,
         this.state.selectedIndex,