Add NULL check for renderBox::layer() on applying zoom level change

Source/core/rendering/RenderBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 236 matching lines @@
             && parent() && !parent()->normalChildNeedsLayout())
             parent()->setChildNeedsLayout();
     }
 
     if (RenderBlock::hasPercentHeightContainerMap() && firstChild()
         && oldHorizontalWritingMode != isHorizontalWritingMode())
         RenderBlock::clearPercentHeightDescendantsFrom(this);
 
     // If our zoom factor changes and we have a defined scrollLeft/Top, we need to adjust that value into the
     // new zoomed coordinate space.
-    if (hasOverflowClip() && oldStyle && newStyle && oldStyle->effectiveZoom() != newStyle->effectiveZoom()) {
+    if (hasOverflowClip() && oldStyle && newStyle && oldStyle->effectiveZoom() != newStyle->effectiveZoom() && layer()) {
         if (int left = layer()->scrollXOffset()) {
             left = (left / oldStyle->effectiveZoom()) * newStyle->effectiveZoom();
             layer()->scrollToXOffset(left);
         }
         if (int top = layer()->scrollYOffset()) {
             top = (top / oldStyle->effectiveZoom()) * newStyle->effectiveZoom();
             layer()->scrollToYOffset(top);
         }
     }
 
@@ skipping 4473 matching lines @@
         return 0;
 
     if (!layoutState && !flowThreadContainingBlock())
         return 0;
 
     RenderBlock* containerBlock = containingBlock();
     return containerBlock->offsetFromLogicalTopOfFirstPage() + logicalTop();
 }
 
 } // namespace WebCore