Make sure failure modes are robust, expand failIfInvalidXML

[kdlong]

cmssw/GeneratorInterface/Core/src/LHEWeightHelper.cc

Lines 33 to 37 in 57b20d3

	if (xmlError != 0) {
	boost::replace_all(fullHeader, "&lt;", "<");
	boost::replace_all(fullHeader, "&gt;", ">");
	xmlError = xmlDoc.Parse(fullHeader.c_str());
	}

This should also be captured under the failIfInvalidXML