logger: use Logger* instead of Logger& to propagate signature using swig

See the comment in IfcLogger.h explaining this.

src/serializers/schema_dependent/XmlSerializer.h

@@ -40,7 +40,7 @@ private:
 
 public:
 	POSTFIX_SCHEMA(XmlSerializer)(IfcParse::IfcFile* file, const std::string& xml_filename, Logger& logger = Logger::Root())
-		: XmlSerializer(0, "", logger)
+		: XmlSerializer(0, "", &logger)
 		, mapping_(ifcopenshell::geometry::impl::mapping_implementations().construct(file, settings_, logger))
 	{
 		this->file = file;