In `pseudo_slave_mode=1` aka "psedo-slave" mode any prepared XA
transaction disconnects from the user session, as if the user
connection drops. The xid of such transaction remains in the server,
and should the prepared transaction be read-only, it is marked.
The marking makes sure that the following termination of the
read-only transaction  ends up with ER_XA_RBROLLBACK.
This did not take place actually for  `pseudo_slave_mode=1` read-only.

Fixed with checking the read-only status of a prepared transaction
at time it disconnects from the `pseudo_slave_mode=1` session, to mark
its xid when that's the case.