flat_mutation_reader: consume_in_thread: always filter.on_end_of_stream on return
flat_mutation_reader: consume_in_thread: always filter.on_end_of_stream on return

Since we're calling _consumer.consume_end_of_stream()
unconditionally when consume_pausable_in_thread returns.

Refs #7623
Refs #7640

Test: unit(dev)
Dtest: materialized_views_test.py:TestMaterializedViews.interrupt_build_process_with_resharding_low_to_half_test

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>
Message-Id: <20210106103024.3494569-1-23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

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