Fix CompactionIterator flag for penultimate level output (#10967)

Fix CompactionIterator flag for penultimate level output (#10967)

Summary:
We were not resetting it in non-debug mode so it could be true once and then stay true for future keys where it should be false. This PR adds the reset logic.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10967

Test Plan:
- built `db_bench` with DEBUG_LEVEL=0
- ran benchmark: `TEST_TMPDIR=/dev/shm/prefix ./db_bench -benchmarks=fillrandom -compaction_style=1 -preserve_internal_time_seconds=100 -preclude_last_level_data_seconds=10 -write_buffer_size=1048576 -target_file_size_base=1048576 -subcompactions=8 -duration=120`
- compared "output_to_penultimate_level: X bytes + last: Y bytes" lines in LOG output
  - Before this fix, Y was always zero
  - After this fix, Y gradually increased throughout the benchmark

Reviewed By: riversand963

Differential Revision: D41417726

Pulled By: ajkr

fbshipit-source-id: ace1e9a289e751a5b0c2fbaa8addd4eda5525329