Avoid taking the negation of an unsigned type in int conversion code.

Though this path is never taken for unsigned ints, MSVC still throws
warning C4146.

Cython/Utility/TypeConversion.c

@@ -676,7 +676,7 @@ static CYTHON_INLINE {{TYPE}} {{FROM_PY_FUNCTION}}(PyObject *x) {
                         if (8 * sizeof(unsigned long) > {{_size}} * PyLong_SHIFT) {
                             __PYX_VERIFY_RETURN_INT({{TYPE}}, {{'long' if _case < 0 else 'unsigned long'}}, {{'-(long) ' if _case < 0 else ''}}{{pylong_join(_size, 'digits')}})
                         } else if (8 * sizeof({{TYPE}}) - 1 > {{_size}} * PyLong_SHIFT) {
-                            return ({{TYPE}}) {{'-' if _case < 0 else ''}}{{pylong_join(_size, 'digits', TYPE)}};
+                            return ({{TYPE}}) {{'((%s)-1)*' % TYPE if _case < 0 else ''}}{{pylong_join(_size, 'digits', TYPE)}};
                         }
                     }
                     break;