repair: initialize row_level_repair: _zero_rows
repair: initialize row_level_repair: _zero_rows

Avoid following UBSAN error:
repair/row_level.cc:2141:7: runtime error: load of value 240, which is not a valid value for type 'bool'

Fixes #5531

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

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