archive_discover

Fixed buffer underrun in cleanup_dirname().

Also fixed that original (unencoded) database and table
names were used to discover archive tables.

mysql-test/r/archive.result:
  A test case for BUG#58205.
mysql-test/t/archive.test:
  A test case for BUG#58205.
mysys/mf_pack.c:
  Fixed buffer underrun in cleanup_dirname(), when
  it gets path like "a/../" (relative path, where
  first directory is to be cut off).
storage/archive/ha_archive.cc:
  Handler discover method gets database and table
  names as is. It must use build_table_filename()
  to get name similar to what it gets on create()
  and open().