[3.12] gh-112087: Fix reduce logic for the empty reverse iterator for list

[corona10]

• Issue: Make list objects thread-safe in --disable-gil builds #112087

[corona10]

/python.exe -m test test_iter -R 3:3 Using random seed: 1549591648 Raised RLIMIT_NOFILE: 256 -> 1024 0:00:00 load avg: 8.69 Run 1 test sequentially 0:00:00 load avg: 8.69 [1/1] test_iter beginning 6 repetitions 123456 ...... == Tests result: SUCCESS ==