When determining whether a SC donated from the notification should be
returned, we must ensure not to try and return a NULL SC to a
notification with not bound SC.
This could occur when a passive server performs a NBSendWait/NBSendRecv
with a notification in the receive phase, where the SC for the receiver
was returned in the send phase and the notification has no bound SC.
Signed-off-by: Curtis Millar <curtis.millar@data61.csiro.au>
6a9e860e4e