Apply behaviour change fix from upstream for previous XPath change.

BUG=58731
TEST=NONE

Review URL: http://codereview.chromium.org/4027006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@63572 0039d316-1c4b-4281-b951-d872f2087c98
xmlXPathCastNodeToString (xmlNodePtr node) {
xmlChar *ret;
    if ((ret = xmlNodeGetContent(node)) == NULL)
	ret = xmlStrdup((const xmlChar *) "");
    return(ret);
}

xmlXPathCastNodeToString (xmlNodePtr node) {
xmlChar *ret;
    if ((ret = xmlNodeGetContent(node)) == NULL)
	ret = xmlStrdup((const xmlChar *) "");
    return(ret);
}
