mutation_reader: Fix abort when streaming more than one range
mutation_reader: Fix abort when streaming more than one range

multi_range_mutation_reader uses fast_forward_to() to skip between
ranges, so we always need to create the underlying reader with with
mutation_reader::forwarding::yes if there is more than one range,
irrespective of whether multi_range_mutation_reader itself will be
forwarded or not.

Fixes #2510.

Introduced in commit 3018df1.

Message-Id: <185a8f68dfdd121f813451c6c7f4ce95c8a60594@scylladb.com>

scylladb/scylla,duarten/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla,duarten/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla