[boost] [extension] Check if basic_type_map is empty

When a library is loaded the return type of shared_library::open() or shared_library::is_open() can be used to detect whether the library was loaded successfully. When shared_library::call() is called the return type can be used to detect whether the exported map function could be called. But is there another function like is_open() which could be called afterwards to check if the map function was called successfully? The datatype basic_type_map only provides get() and no empty(). It would be required to call get() first and operate on the returned std::map type to see if it contains any factories? Boris