Don't add empty NodeRegion, because it will never receive touch events anyway

Summary: Small optimization that prevents empty NodeRegions from being collected. Those will never receive touch events anyway, so why bother allocating memory and iterating over them?

Reviewed By: ahmedre

Differential Revision: D2816355

ReactAndroid/src/main/java/com/facebook/react/flat/StateBuilder.java

@@ -150,6 +150,11 @@ import com.facebook.react.uimanager.events.EventDispatcher;
       float top,
       float right,
       float bottom) {
+    if (left == right || top == bottom) {
+      // no point in adding an empty NodeRegion
+      return;
+    }
+
     node.updateNodeRegion(left, top, right, bottom);
     mNodeRegions.add(node.getNodeRegion());
   }