error when using cache_size = 1

[Pomyk]

With cache_size = 1 I get the following error:

** (MatchError) no match of right hand side value: nil
    (mariaex) lib/mariaex/lru_cache.ex:57: Mariaex.LruCache.take_oldest/1
    (mariaex) lib/mariaex/protocol.ex:351: Mariaex.Protocol.prepare_lookup/2
    (mariaex) lib/mariaex/protocol.ex:336: Mariaex.Protocol.handle_prepare/3
    (mariaex) lib/mariaex/protocol.ex:328: Mariaex.Protocol.handle_prepare/3
    (db_connection) lib/db_connection.ex:966: DBConnection.handle/4
    (db_connection) lib/db_connection.ex:1067: anonymous fn/4 in DBConnection.run_prepare_execute/4
    (db_connection) lib/db_connection.ex:1150: anonymous fn/4 in DBConnection.run_meter/5
    (db_connection) lib/db_connection.ex:1207: DBConnection.run_begin/3
    (db_connection) lib/db_connection.ex:592: DBConnection.prepare_execute/4
    (ecto) lib/ecto/adapters/mysql/connection.ex:22: Ecto.Adapters.MySQL.Connection.execute/4
    (ecto) lib/ecto/adapters/sql.ex:256: Ecto.Adapters.SQL.sql_call/6
    (ecto) lib/ecto/adapters/sql.ex:448: Ecto.Adapters.SQL.sql_call!/6
    (ecto) lib/ecto/adapters/sql.ex:420: Ecto.Adapters.SQL.do_execute/6
    (ecto) lib/ecto/repo/queryable.ex:133: Ecto.Repo.Queryable.execute/5
    (ecto) lib/ecto/repo/queryable.ex:37: Ecto.Repo.Queryable.all/4```

Tested on mariaex 0.8.4 and 0.8.3. With cache_size = 2 there are no errors.