cdc: fix preimage query for static rows
cdc: fix preimage query for static rows

For static rows, we need to fetch at least one row from its partition in
order to compute its preimage.

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