Fix a crash in ChromeActiveDocument::IOleObject_SetClientSite....

chrome_frame/chrome_active_document.cc

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Implementation of ChromeActiveDocument
 #include "chrome_frame/chrome_active_document.h"
 
 #include <hlink.h>
 #include <htiface.h>
 #include <initguid.h>
@@ skipping 368 matching lines @@
     IOleClientSite* client_site) {
   if (client_site == NULL) {
     ChromeActiveDocument* cached_document = g_active_doc_cache.Get();
     if (cached_document) {
       DCHECK(this == cached_document);
       g_active_doc_cache.Set(NULL);
       cached_document->Release();
     }
 
     ScopedComPtr<IDocHostUIHandler> doc_host_handler;
-    doc_host_handler.QueryFrom(doc_site_);
+    if (doc_site_) {
+      doc_host_handler.QueryFrom(doc_site_);
+    }
 
     if (doc_host_handler.get()) {
       doc_host_handler->HideUI();
     }
 
     doc_site_.Release();
     in_place_frame_.Release();
   }
 
   if (client_site != m_spClientSite)
@@ skipping 608 matching lines @@
   ScopedComPtr<IWebBrowser2> web_browser2;
   DoQueryService(SID_SWebBrowserApp, m_spClientSite, web_browser2.Receive());
   DCHECK(web_browser2);
 
   if (web_browser2) {
     web_browser2->GoBack();
   }
   return 0;
 }