bpo-33234: Simplify list_preallocate_exact()

Objects/listobject.c

@@ -81,26 +81,15 @@ static int
 list_preallocate_exact(PyListObject *self, Py_ssize_t size)
 {
  assert(self->ob_item == NULL);
+ assert(size > 0);
 
- PyObject **items;
- size_t allocated;
-
- allocated = (size_t)size;
- if (allocated > (size_t)PY_SSIZE_T_MAX / sizeof(PyObject *)) {
- PyErr_NoMemory();
- return -1;
- }
-
- if (size == 0) {
- allocated = 0;
- }
- items = (PyObject **)PyMem_New(PyObject*, allocated);
+ PyObject **items = PyMem_New(PyObject*, size);
  if (items == NULL) {
  PyErr_NoMemory();
  return -1;
  }
  self->ob_item = items;
- self->allocated = allocated;
+ self->allocated = size;
  return 0;
 }