During Connection destruction it can happen that the socket is
deleted, but the actual handler is still running and tries to
write to that socket (in which case it passes a nullptr to
DataStream). This is caused by the issue described in #376822.

To prevent the crash in this case (until the root cause is fixed)
the DataStream throws an exception if its used without a valid
device. This will effectively cause execution to leave the Handler
and return.

BUG: 376385
FIXED-IN: 5.4.3