Add missing null check

Bug: 13635394
 mDisplayListData can be null, make sure
 to check for that before trying to walk through the
 children list in updateProperties

Change-Id: I8d97b1656c1acf47b7c5df8a8771b0f30907261d

libs/hwui/RenderNode.cpp

@@ -99,9 +99,11 @@ void RenderNode::updateProperties() {
         mProperties = mStagingProperties;
     }
 
-    for (size_t i = 0; i < mDisplayListData->children.size(); i++) {
-        RenderNode* childNode = mDisplayListData->children[i]->mDisplayList;
-        childNode->updateProperties();
+    if (mDisplayListData) {
+        for (size_t i = 0; i < mDisplayListData->children.size(); i++) {
+            RenderNode* childNode = mDisplayListData->children[i]->mDisplayList;
+            childNode->updateProperties();
+        }
     }
 }