[HUBZERO][#6117][PLG_TAGS_PUBLICATIONS][1.2.2] fix to php notice
[HUBZERO][#6119][LIB_JOOMLA] Stop trying to use nonexistent var.
[HUBZERO][#6125][COM_SYSTEM] Have component throw a 404 since there's no front-end yet.
[HUBZERO][#6120][PLG_USAGE_TOOLS] Check for property existence before attempted use