refs #895, also log when parts are empty

* added empty flag
* move logging into own function (because it is called in multiple places now)

src/blackmisc/simulation/interpolator.h

@@ -88,6 +88,9 @@ namespace BlackMisc
         private:
             CInterpolationLogger *m_logger = nullptr;
 
+            //! Log parts
+            void logParts(qint64 timestamp, const Aviation::CAircraftParts &parts, bool empty, bool log);
+
             Derived *derived() { return static_cast<Derived *>(this); }
             const Derived *derived() const { return static_cast<const Derived *>(this); }
         };