[3.11] 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]

(.oss) ➜ cpython git:(gh-112087-3.11) ✗ ./python.exe -m test test_iter -R 3:3 Using random seed: 3663832972 Raised RLIMIT_NOFILE: 256 -> 1024 0:00:00 load avg: 6.95 Run 1 test sequentially 0:00:00 load avg: 6.95 [1/1] test_iter beginning 6 repetitions 123456 ...... == Tests result: SUCCESS == 1 test OK. Total duration: 1.1 sec Total tests: run=56 Total test files: run=1/1 Result: SUCCESS