If a table that is not replicated to a certain DC (rf=0) is accessed
with LOCAL_QUORUM on that DC the current code will crash since the
'targets' array will be empty and read executor does not handle it.
Fix it by replying with empty result.
Fixes#8354
Message-Id: <YGro+l2En3fF80CO@scylladb.com>
(cherry picked from commit cd24dfc7e5)
[avi: re-added virtual keyword when backporting, since
4.4 and below don't have 020da49c89]
4200e52444