CodeQL: Return pointers not checked

[PLohrmannAMD]

CodeQL (a code quality/security tool) points out a handful of alerts in tinyxml2.

In each of the seven Query*Text methods, the const char* t = FirstChild()->Value(); return value is not null-checked.

For example:

XMLError XMLElement::QueryIntText( int* ival ) const
{
    if ( FirstChild() && FirstChild()->ToText() ) {
        const char* t = FirstChild()->Value();
        if ( XMLUtil::ToInt( t, ival ) ) {
            return XML_SUCCESS;
        }
        return XML_CAN_NOT_CONVERT_TEXT;
    }
    return XML_NO_TEXT_NODE;
}

Likewise, in DeepClone(), the XMLNode* childClone = child->DeepClone(target); is not null-checked in release builds, although in debug builds the TIXMLASSERT() would detect it. If one of the child->DeepClone() fails, the shallow cloned object at the top should be deleted.

XMLNode* XMLNode::DeepClone(XMLDocument* target) const
{
	XMLNode* clone = this->ShallowClone(target);
	if (!clone) return 0;

	for (const XMLNode* child = this->FirstChild(); child; child = child->NextSibling()) {
		XMLNode* childClone = child->DeepClone(target);
		TIXMLASSERT(childClone);
		clone->InsertEndChild(childClone);
	}
	return clone;
}