row_cache: autoupdating_underlying_reader: fast_forward_to: capture snapshot by value when updating reader
row_cache: autoupdating_underlying_reader: fast_forward_to: capture snapshot by value when updating reader

Currently we capture the snapshot mutation_source by reference
for calling create_underlying_reader after closing the reader.
However, if close_reader yields, the snapshot reference passed
may be gone, so capture it by value instead.

Fixes #8848

Test: unit(dev)
DTest: restore_snapshot_using_old_token_ownership_test(debug)

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>
Message-Id: <20210613104232.634621-1-23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla