Reports Expl: Fixed a page rendering issue due to a non-existent node

Set the active node to be "root" when there is a non-existent custom
report node as a result of a delete action on the only existing custom
report

https://bugzilla.redhat.com/show_bug.cgi?id=1112574
Merge pull request #93 from AparnaKarve/bz1112574_setnode_after_lastreport_delete

Reports Explorer: Fixed a page rendering issue due to a non-existent custom report node