INT-3290 Fix TCP Deserializer for 0 Length Message

ByteArraySingleTerminatorSerializer does not support multiple
subsequent terminators (zero length messages).

JIRA: https://jira.springsource.org/browse/INT-3290

* Add unit test to verify bug.
* Fix bug.

Polishing:

* Remove test for `n >= 0`; n cannot be < 0 here
* Move test case to `DeserializationTests`

Conflicts:

	spring-integration-ip/src/test/java/org/springframework/integration/ip/tcp/serializer/DeserializationTests.java

Resolved.