JIRA: https://jira.spring.io/browse/INT-4452
This is pretty typical in practice to get a `groupTimeout` to be
evaluated to a negative value: some business decisions, sensitive
calculations and so on.
* Treat any non-positive `groupTimeout` as a signal to expire group
immediately without scheduling.
Only `null` is considered as a signal do nothing for the current message
* Polishing for some tests for better performance - saves some execution
time
13510df575