Bug #34002 uninitialized Rows_examined for some admin queries

such as quit and shutdown

Logging to slow log can produce an undetermined value for
Rows_examined in special cases. In debug mode this manifests
itself as any of the various marker values used to mark
uninitialized memory on various platforms.

If logging happens on a THD object that hasn't performed any
row reads (on this or any previous connections), the
THD::examined_row_count may be uninitialized. This patch adds
initialization for this attribute.

No automated test cases are added, as for this to be
meaningful, we need to ensure that we're using a THD
fulfilling the above conditions. This is hard to do in the
mysql-test-run framework. The patch has been verified
manually, however, by restarting mysqld and running the test
included with the bug report.

sql/sql_class.cc

@@ -546,6 +546,7 @@ THD::THD()
    first_successful_insert_id_in_prev_stmt_for_binlog(0),
    first_successful_insert_id_in_cur_stmt(0),
    stmt_depends_on_first_successful_insert_id_in_prev_stmt(FALSE),
+   examined_row_count(0),
    global_read_lock(0),
    is_fatal_error(0),
    transaction_rollback_request(0),