Do not crash when ScrollView snapToOffsets is empty

Summary:
The value of the `ScrollView.snapToOffsets` property can be an empty array (most likely an issue in the product code), which will crash the app. This diff adds a check to prevent crashing in this scenario and falling back to the default snap behaviour.

Changelog:
[Android][Fixed] - Do not crash when ScrollView snapToOffsets is empty

Reviewed By: sammy-SC

Differential Revision: D24502365

fbshipit-source-id: c63b8e3b8f2fb323ebd6c962ee628015934d8e11

ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.java

@@ -817,7 +817,7 @@ private void flingAndSnap(int velocityX) {
     }
 
     // get the nearest snap points to the target offset
-    if (mSnapOffsets != null) {
+    if (mSnapOffsets != null && !mSnapOffsets.isEmpty()) {
       firstOffset = mSnapOffsets.get(0);
       lastOffset = mSnapOffsets.get(mSnapOffsets.size() - 1);