Restart of mcsRebuildEM-rebuilt MCS crashes server and does not restore anything

The steps to reproduce:

1. on clean MDB/MCS installation create a table with single LONGTEXT column: mariadb test -e "create table t (x longtext) engine = columnstore;"
2. insert a bunch of data: mariadb test -e "insert into t( x ) select concat(seq, repeat('zuka',4000000)) from seq_1_to_10000;"
3. stop the columnstore: systemctl stop mariadb-columnstore
4. delete EM files: rm -f /var/lib/columnstore/data1/systemFiles/dbrm/BRM_saves*_em
5. perform EM rebuild: mcsRebuildEM -v
6. start MCS again: systemctl start mariadb-columnstore
7. check whether there is something in the table and get "server connection" error: mariadb test -e "select count( * ) from t;"
8. check whether server is running: pidof mariadbd - it does not.
9. restart MariaDB service: systemctl restart mariadb
10. # check whether there is something in the table and get "internal error" error from MCS: mariadb test -e "select count( * ) from t;"

That's about it.