Reset java state in jni reset method

Summary: This state was never reset when we switched to doing reset in C instead of re-allocating.

Differential Revision: D4081049

fbshipit-source-id: 0b9ad70339ad906ad5219ad2679329cfe2fd7abc

csharp/Facebook.CSSLayout/CSSNode.cs

@@ -44,6 +44,9 @@ namespace Facebook.CSSLayout
 
         public void Reset()
         {
+            _measureFunction = null;
+            _data = null;
+
             Native.CSSNodeReset(_cssNode);
         }