Lists of "negative" length are also empty, and that's the case we special-case...

Lists of "negative" length are also empty, and that's the case we special-case later in an inline function, so use the same condition for consistency and easy C compiler optimisation.

See https://github.com/cython/cython/pull/4734

Cython/Utility/ObjectHandling.c

@@ -858,7 +858,7 @@ static CYTHON_INLINE PyObject* __Pyx_Py{{type}}_GetSlice(
     Py_ssize_t length = Py{{type}}_GET_SIZE(src);
     __Pyx_crop_slice(&start, &stop, &length);
 {{if type=='List'}}
-    if (length == 0) {
+    if (length <= 0) {
         // Avoid undefined behaviour when accessing `ob_item` of an empty list.
         return PyList_New(0);
     }