KahaDB checkpoint needs to fail fast in the event of journal write failure

KahaDB checkpoint does some async updated to the journal and syncs to the index. However the async journal updates can error out and not get reported leading to the index metadata being stale. This can lead to reading an invalid location on restart which may result in full recovery of the index.

Any exception from the async store needs to cause the checkpoint to fail.

In addition, on reading a corrupt location, we can do a sanity check to avoid a potential OOM by validating the size before allocation.