BUG: Fix(up) incorrect return in SetItemFast
BUG: Fix(up) incorrect return in SetItemFast

Sorry, my previous fix was cursed (not running the tests), now I
saw the compiler warning, and I suppose it would be good for the
tests to run error paths.

cython/cython,da-woods/cython,cython/cython,scoder/cython,cython/cython,scoder/cython,scoder/cython,cython/cython,da-woods/cython,scoder/cython,da-woods/cython,da-woods/cython