Investigate write failure handling in MutationLog

void MutationLog::updateInitialBlock() {

    if (readOnly) {

        throw std::logic_error("MutationLog::updateInitialBlock: Not valid on "

                               "a read-only log");

    }

    if (!isOpen()) {

        throw std::logic_error("MutationLog::updateInitialBlock: Not valid on "

                               "a closed log");

    }

    needWriteAccess();

    std::vector<uint8_t> buf(MIN_LOG_HEADER_SIZE);

    memcpy(buf.data(), &headerBlock, sizeof(headerBlock));

    ssize_t byteswritten = pwrite(file, buf.data(), buf.size(), 0);

    if (byteswritten != ssize_t(buf.size())) {

        throw WriteException("Failed to update header block");

    }

}

[ns_server:info,2022-06-12T02:00:01.761Z,babysitter_of_ns_1@cb.local:<0.129.0>:ns_port_server:log:221]memcached<0.129.0>: 2022-06-12T02:00:01.559986+00:00 CRITICAL *** Fatal error encountered during exception handling ***

memcached<0.129.0>: 2022-06-12T02:00:01.562845+00:00 CRITICAL Caught unhandled std::exception-derived exception. what(): Failed to update header block

memcached<0.129.0>: terminate called after throwing an instance of 'MutationLog::WriteException'

memcached<0.129.0>:   what():  Failed to update header block

[ns_server:info,2022-06-12T02:00:02.002Z,babysitter_of_ns_1@cb.local:<0.129.0>:ns_port_server:log:221]memcached<0.129.0>: 2022-06-12T02:00:01.848051+00:00 CRITICAL Breakpad caught a crash (Couchbase version 7.0.3-7031). Writing crash dump to /opt/couchbase/var/lib/couchbase/crash/6320c9de-0d65-49b7-3d99c785-adaed8c2.dmp before terminating.

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