Incorrect exception handling in CoreGroupCommunicationService#handle

org/jboss/as/clustering/impl/CoreGroupCommunicationService#handle catches and hides any internal exceptions, and just returns null instead.

This breaks callers of CoreGroupCommunicationService when they get a null value where it's not expected (after verifying that the response was not flagged as an exception)

java.lang.NullPointerException
at org.jboss.as.clustering.lock.AbstractClusterLockSupport.lock(AbstractClusterLockSupport.java:157)

It also catches an exception from the called method, and returns it as the return value, instead of just throwing it as an exception so it can be properly returned as an exception inside JGroups' RequestCorrelator.