The error occurs in Py_Main(), on _PyUnicode_AsString(commandObj). The
problem is that _PyUnicode_AsString() is not checked for error. Here is
a patch fixing two errors:
 - display on error message instead of a crash on
_PyUnicode_AsString(commandObj) failure
 - don't call Py_DECREF(commandObj) if commandObj is NULL
(PyUnicode_FromWideChar error, a different error)

My patch also includes a test. The test should be moved somewhere else,
but I don't know where.