Renamed event->featureChanged.linedevice -> event->featureChanged.optional_linedevice && event->lineStatusChanged.device -> event->lineStatusChanged.optional_device, to make it clear that they do not always have to be set. Prevent retaining possible d=NULL when creating lineStatusChanged event in sccp_indicate. Update comment to reflect the optional status of some of the event arguments

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5060 43c1dc8c-776e-4df2-8ef1-6e829299be21