Calcite engine. Memory leak in MailboxRegistryImpl#remotes on JOINs

When JOIN relational operator is executed, downstream of JOIN can be closed if only one side of JOIN is already drained (see last lines of MergeJoinNode.InnerJoin#join, for example). In this case query can be prematurely closed, and after this, message for another side of join can arrive and register new Inbox (see ExchangeServiceImpl#onMessage(UUID, QueryBatchMessage)), that never will be unregistered.