MDEV-13898 Corruption during online table-rebuilding ALTER of ROW_FORMAT=REDUNDANT tables

This bug is a regression caused by the code refactoring in
commit f5a833c3. It was not present
in any release of the MariaDB server. The bug affects table-rebuilding
ALTER TABLE when the source table is in ROW_FORMAT=REDUNDANT and
contains no virtual columns.

row_log_table_low_redundant(): Log virtual column data only if
virtual columns are present.