m_status == DA_OK

Reading from information_scema.tables or information_schema.columns
may cause assertion failure in debug builds. This may happen under
rare circumstances when information_schema fails to get information
about a table (e.g. when a connection is killed).

This happens because open_normal_and_derived_tables() can return an
error without setting an error message in THD. But information_schema
attempts to get an error message from THD unconditionally.

With this fix information_schema attempts to get an error message
from THD only in case error message is set in THD.


mysql-test/r/information_schema.result:
  A test case for BUG#34656.
mysql-test/t/information_schema.test:
  A test case for BUG#34656.
sql/item_func.cc:
  Set proc info to "User sleep".
sql/sql_show.cc:
  open_normal_and_derived_tables() can return an error without
  setting an error message in THD. That means we must access
  error message conditionally, only in case thd->is_error() is
  true.