Adding an non-empty set of sstables as the set of all sstables in
an sstable_set could cause inconsistencies with the values returned
by select_sstable_runs because the _all_runs map would still be
initialized empty. For similar reasons, the provided sstable_set_impl
should also be empty.
Dispel doubts by removing the unordered_set from the constructor, and
adding a check of emptiness of the sstable_set_impl.
Signed-off-by: Wojciech Mitros <wojciech.mitros@scylladb.com>
e1b494633b