devel/py-jcc: unbreak with clang 4.0

jcc/sources/JArray.cpp:315:66: error: ordered comparison between pointer and zero ('PyObject *' (aka '_object *') and 'int')

PyList_Type.tp_as_sequence->sq_inplace_concat(list, arg) < 0)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~

jcc/sources/JArray.cpp:330:64: error: ordered comparison between pointer and zero ('PyObject *' (aka '_object *') and 'int')

PyList_Type.tp_as_sequence->sq_inplace_repeat(list, n) < 0)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~

Reported by: antoine (via exp-run)