Reset xmlSetGenericErrorFunc after use

...otherwise, unrelated libxml2 clients that try to report errors during exit
can fail if this function is still set but the infrastructure behind it is
already gone.

Change-Id: I7c41fb6770dbff27a71b4b0f82330c608e6e8363

unoxml/source/xpath/xpathapi.cxx

@@ -391,6 +391,7 @@ namespace XPath
         xmlChar *xStr = (xmlChar*)o1.getStr();
         ::boost::shared_ptr<xmlXPathObject> const xpathObj(
                 xmlXPathEval(xStr, xpathCtx.get()), xmlXPathFreeObject);
+        xmlSetGenericErrorFunc(NULL, NULL);
         if (0 == xpathObj) {
             // OSL_ENSURE(xpathCtx->lastError == NULL, xpathCtx->lastError->message);
             throw XPathException();