INT-3433 commit

INT-3433: Fixed NIO deadlock (or timout if the CallerBlocksPolicy is used) with Bounded ThreadPoolTaskExecutor.

JIRA: https://jira.spring.io/browse/INT-3433

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Sure, it's not necessary. I just thought that it should make an assembler thread yield immediately after it received a message, so messages from different clients received more evenly, like it was when a new assembler thread was started instead of the loop. I can be wrong here though.