RGW/multisite/RGWListRemoteBucketCR: clear reused bucket_list_result to avoid stale...

RGW/multisite/RGWListRemoteBucketCR: clear reused bucket_list_result to avoid stale listings

RGWBucketFullSyncCR could spin indefinitely when the source bucket was
already deleted. The coroutine reused a bucket_list_result member, and
RGWListRemoteBucketCR populated it without clearing prior state. Stale
entries/is_truncated from a previous iteration caused the loop to
continue even after the bucket no longer existed.

Fix by clearing the provided bucket_list_result at the start of
RGWListRemoteBucketCR (constructor), ensuring each listing starts from a
clean state and reflects the current remote bucket contents.

This prevents the infinite loop and returns correct results when the
bucket has been deleted.

Fixes: https://tracker.ceph.com/issues/73799
Signed-off-by: Oguzhan Ozmen <oozmen@bloomberg.net>