ibuf_restore_pos(): Do not issue any messages if the tablespace
is being dropped or truncated. In MariaDB 10.2, TRUNCATE TABLE
would not change the tablespace ID, and therefore the tablespace
would be found, even though TRUNCATE is in progress.

Furthermore, do not commit suicide if restoring the change buffer
cursor fails. The worst that could happen is that a secondary index
becomes corrupted due to incomplete change buffer merge.