Added a check for a NULL nsIDeviceContextSpec. This happens when the user "cancels"

out of the print dialog.

webshell/src/nsDocumentViewer.cpp

@@ -458,6 +458,7 @@ NS_IMETHODIMP DocumentViewerImpl :: Print(void)
 
     factory->CreateDeviceContextSpec(nsnull, devspec, PR_FALSE);
 
+    if (nsnull != devspec) {
       dx = mPresContext->GetDeviceContext();
 
       if (NS_OK == dx->GetDeviceContextFor(devspec, newdx))
@@ -531,6 +532,7 @@ NS_IMETHODIMP DocumentViewerImpl :: Print(void)
       }
 
       NS_RELEASE(dx);
+    }
     NS_RELEASE(factory);
   }