[docs] PyModule_GetDict() claims it can never fail, but it can (issue 12946)

[stephane at wirtel.be]

http://bugs.python.org/review/12946/diff/18078/Doc/c-api/module.rst
File Doc/c-api/module.rst (right):

http://bugs.python.org/review/12946/diff/18078/Doc/c-api/module.rst#newcode64
Doc/c-api/module.rst:64: :exc:`SystemError` is raised and *NULL* is
returned.
The assert will raise a SystemError ?

http://bugs.python.org/review/12946/