Comment 4 for bug 1281104

Based on the libxml2 document (http://xmlsoft.org/threads.html), xmlCleanupParser() should be called only once. In openclipart.cpp, it is called each time we update the search list.

The attached patch moves xmlCleanupParser() to the dialog's destructor.
Tested successfully on Windows XP and Crunchbang Waldorf, Inkscape trunk revision 13033.