Fix custom cursors on Mac. Null and 0 turn out not to be opposites....

webkit/api/src/WebImageCG.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 58 matching lines @@
     m_imageRef = 0;
 }
 
 void WebImage::assign(const WebImage& image)
 {
     assign(image.m_imageRef);
 }
 
 bool WebImage::isNull() const
 {
-    return m_imageRef != 0;
+    return m_imageRef == 0;
 }
 
 WebSize WebImage::size() const
 {
     return WebSize(CGImageGetWidth(m_imageRef), CGImageGetHeight(m_imageRef));
 }
 
 WebImage::WebImage(const PassRefPtr<Image>& image)
     : m_imageRef(0)
 {
@@ skipping 10 matching lines @@
     return *this;
 }
 
 void WebImage::assign(CGImageRef imageRef)
 {
     CGImageRelease(m_imageRef);
     CGImageRetain(m_imageRef = imageRef);
 }
 
 } // namespace WebKit