Currently, when a module implements m_traverse(), m_clear() or m_free(), these methods can be called with md_state=NULL even if the module implements the "Multi-phase extension module initialization" API (PEP 489).

I'm talking about these module methods:

* tp_traverse: module_traverse() calls md_def->m_traverse() if m_traverse is not NULL
* tp_clear: module_clear() calls md_def->m_clear() if m_clear is not NULL
* tp_dealloc: module_dealloc() calls md_def->m_free() is m_free is not NULL

Because of that, the implementation of these methods must check manually if md_state is NULL or not.

I propose to change module_traverse(), module_clear() and module_dealloc() to not call m_traverse(), m_clear() and m_free() if md_state is NULL and m_size > 0.

"m_size > 0" is an heuristic to check if the module implements the "Multi-phase extension module initialization" API (PEP 489). For example, the _pickle module doesn't fully implements the PEP 489: m_size > 0, but PyInit__pickle() uses PyModule_Create().

See bpo-32374 which documented that "m_traverse may be called with m_state=NULL" (GH-5140).