improve error handling in __Pyx_init_sys_getdefaultencoding_params()

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extra : transplant_source : %CD%DB%8CT%85r%FF%0B%1C%60%B3%CD%F8%16%D8%E3%EC%C7%0BL
fix ASCII compatibility check in __Pyx_init_sys_getdefaultencoding_params(): strncmp() stops at first NUL byte which is the first byte in this case (i.e. no comparison is done at all)

--HG--
extra : transplant_source : A%2B%5BO%82%05%F7%DEm/%8Ao%08%121%96%8Ao%AB%8C
fix ASCII compatibility check in __Pyx_init_sys_getdefaultencoding_params(): strncmp() stops at first NUL byte which is the first byte in this case (i.e. no comparison is done at all)
merge 0.20.x branch into master