I can't quite figure out how we were trying to write a sstable with
the large data handler already stopped, but the backtrace suggests a
good place to add extra checks.
This patch adds two check. One at the start and one at the end of
sstable::write_components. The first one should give us better
backtraces if the large_data_handler is already stopped. The second
one should help catch some race condition.
Refs: #5470
Message-Id: <20191231173237.19040-1-espindola@scylladb.com>
75817d1fe7