INT-3066 Fix NPE During Connection Recovery

The JmsOutboundGateway's Listener container could throw
an NPE during connection recovery - while logging recovery
status.

The log attempts to include the destination description which
throws the NPE if there is no destination yet established.

Only attempt to get the description if the destination has
been established. And, even then, use a try/catch block
to prevent the NPE. Log the destination as 'unknown' in this
case.

Add a test case to detect the NPE by adding an ErrorHandlingTaskExecutor.

No errors should be detected with the fix in place.