Concatenates the invocation lists of the specified multicast (combinable) delegate and the current multicast (combinable) delegate.
A new multicast (combinable) delegate with an invocation list that concatenates the invocation list of the current multicast (combinable) delegate and the invocation list of d, or the current multicast (combinable) delegate if d is null.
This method applies only if the current delegate is multicast (combinable).
The current implementation simply throws a MulticastNotSupportedException.
The invocation list can contain duplicate entries; that is, entries that refer to the same method on the same object.