MDEV-14401: Stored procedure that declares a handler that catches ER_LOCK_DEADLOCK error causes thd->is_error() assertion

This was missing bug fix from MySQL wsrep i.e. Galera.
Problem was that if stored procedure declares a handler that
catches deadlock error, then the error may have been
cleared in method sp_rcontext::handle_sql_condition().
Use wsrep_conflict_state correctly to determine is the
error already sent to client.

Add test case for both this bug and MDEV-12837: WSREP: BF
lock wait long. Test requires both fixes to pass.