Ref T185 Enable spline interpolation with only one position update,

by just copying it three times, so planes can be rendered without waiting for more updates.

src/blackmisc/aviation/aircraftsituationlist.cpp

@@ -27,5 +27,9 @@ namespace BlackMisc
             CSequence<CAircraftSituation>(other)
         { }
 
+        CAircraftSituationList::CAircraftSituationList(std::initializer_list<CAircraftSituation> il) :
+            CSequence<CAircraftSituation>(il)
+        { }
+
     } // namespace
 } // namespace