os/bluestore/bluefs: Fix data corruption in truncate()

os/bluestore/bluefs: Fix data corruption in truncate()

It is possible to create condition in which a BlueFS contains file that is corrupted.
It can happen when BlueFS replay log is on device A and we just wrote to device B and truncated file.

Scenario:
1) write to file h1 on SLOW device
2) flush h1 (initiate transfer, but no fdatasync yet)
3) truncate h1
4) write to file h2 on DB
5) fsync h2 (forces replay log to be written, after fdatasync to DB)
6) poweroff

Fixes: https://tracker.ceph.com/issues/53129
Signed-off-by: Adam Kupczyk <akupczyk@redhat.com>