Two bugs here:

1. CHECKSUM TABLE asserted that all fields in the table are arranged
   sequentially in the record, but virtual columns are always at the
   end, violating this assertion
2. virtual columns were not calculated for CHECKSUM, so CHECKSUM
   was using, essentially, garbage left from the previous statement.
   (that's why the test must use INSERT IGNORE to have this "previous
   statement" mark vcols not null)

Fix: don't include virtual columns into the table CHECKSUM. Indeed,
they cannot be included as the engine does not see virtual columns,
so in-engine checksum cannot include them, meaning in-server checksum
should not either