sstables: Write empty static rows when there are static columns in the table.
sstables: Write empty static rows when there are static columns in the table.

This is consistent with what Cassandra does.

Fixes #3900.

Signed-off-by: Vladimir Krivopalov <dc9186a06078733915a6fcbab34e59120be2b484@scylladb.com>

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