fix core dumped err when loadplugin

plugins/preferred_layer.cpp

@@ -25,11 +25,11 @@ unsigned char PreferredLayer::interpretValue(unsigned char value)
 }
 
 // Export factory function
-static PluginLayerPtr create_preferred_plugin() {
+static std::shared_ptr<Layer> create_preferred_plugin() {
     return std::make_shared<PreferredLayer>();
 }
 
 // Alias cho Boost.DLL (nếu muốn dùng boost::dll::import_alias)
-BOOST_DLL_ALIAS(create_preferred_plugin, create_plugin)
+BOOST_DLL_ALIAS(create_preferred_plugin, create_preferred_layer)
 
 }