table

The MERGE table storage engine does not support the HA_CAN_SQL_HANDLE feature
and any attempt to open the merge table will fail with ER_ILLEGAL_HA.

After an error occurred the tables that was opened must be closed again
or they will be left in an inconsistent state. However, the assumption
made in the code for closing and register handler tables was that only
one table will be opened, and this is not true for MERGE tables which
will cause multiple tables to open.

The next time a SELECT operation was issued on the merge table it
caused the system to freeze.

This patch fixes this issue by making sure that all tables which
are opened also are closed in the event of an error.


mysql-test/r/merge.result:
  Added test case for bug 45781
mysql-test/t/merge.test:
  Added test case for bug 45781
sql/sql_handler.cc:
  * mysql_ha_open() was never ment to open more than one table. If we encounter more tables, we should
    close all tables related to the current substatement and raise an exception.