INT-3227 Fix Race Condition for WARN Log

JIRA: https://jira.springsource.org/browse/INT-3227

In MessagingTemplate.TemporaryReplyChannel, it was possible
the `clientHasReceived` boolean could be set by the other
thread after normal message receipt, but before the sender
tests it for the purpose of emitting a duplicate reply log
message.

Capture the boolean value of `clientHasReceived` before
counting down the latch.