never attach null functor

bug:6412902

Change-Id: I26a5f80ae13cc19df3daa4d4e7e5401778f76dbb

Author: ChrisCraik

core/java/android/webkit/WebViewClassic.java

@@ -7890,7 +7890,9 @@ void setNewPicture(final WebViewCore.DrawData draw, boolean updateBaseLayer) {
         ViewRootImpl viewRoot = mWebView.getViewRootImpl();
         if (mWebView.isHardwareAccelerated() && viewRoot != null) {
             functor = nativeGetDrawGLFunction(mNativeClass);
-            viewRoot.attachFunctor(functor);
+            if (functor != 0) {
+                viewRoot.attachFunctor(functor);
+            }
         }
 
         if (functor == 0