engine: fix repeatedly duplicated events in subtabs

Commit f6772a1 missed an 'else' that caused all events subtabs to repeatedly duplicate
their contents, on every refresh. So every 5 seconds all events were re-sent to the UI,
and the list would double, triple, etc.

Change-Id: I1862bbece2e527efd9068f098ad9212cfd868b4f
Bug-Url: https://bugzilla.redhat.com/1048916
Signed-off-by: Greg Sheremeta <gshereme@redhat.com>