MB-11447: Don't close db handle if rollback header fails

This happens automatically in couchstore and will cause a segfault
if we try to close the handle again.

Change-Id: I4e0f756749951ac869861fc150303b9df594ca65
Reviewed-on: http://review.couchbase.org/38377
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>