Fix NullPointerException in ReactShadowNode.toString()

Summary:
Fix `NullPointerException` in `ReactShadowNode.toString`
Simplified `ReactShadowNode.hasNewLayout` since I was already in there

It seems to me unlikely that this bug impacts anything but the debugging experience, so no biggie.
Closes #12953

Differential Revision: D4739215

fbshipit-source-id: 94955cc783216fdb8868fc8d08010e0d8a238052

Author: Petter Hesselberg

ReactAndroid/src/main/java/com/facebook/react/uimanager/ReactShadowNode.java

@@ -372,7 +372,7 @@ public void calculateLayout() {
   }
 
   public final boolean hasNewLayout() {
-    return mYogaNode == null ? false : mYogaNode.hasNewLayout();
+    return mYogaNode != null && mYogaNode.hasNewLayout();
   }
 
   public final void markLayoutSeen() {
@@ -770,7 +770,11 @@ public void setMeasureFunction(YogaMeasureFunction measureFunction) {
 
   @Override
   public String toString() {
-    return mYogaNode.toString();
+    if (mYogaNode != null) {
+      return mYogaNode.toString();
+    }
+
+    return getClass().getSimpleName() + " (virtual node)";
   }
 
   public void dispose() {