The code in Type_handler_blob****::make_conversion_table_field()
erroneously assumed that row format replication uses
MYSQL_TYPE_TINYBLOB, MYSQL_TYPE_BLOB, MYSQL_TYPE_MEDIUMBLOB,
MYSQL_TYPE_LONGBLOB type codes to tranfer BLOB variations.

In fact, all BLOB variations use MYSQL_TYPE_BLOB as the type
code, while the BLOB packlength (1,2,3 or 4) it tranferred
in metadata.

The bug was introduced by  aee06808
(MDEV-9238 Wrap create_virtual_tmp_table() into a class, split into different steps)