Fixed warnings as mentioned in

https://dev.vatsim-germany.org/boards/22/topics/2587?r=2598#message-2598
and found by
+win32-msvc*:QMAKE_CXXFLAGS_WARN_ON *= /Wall /W3 /wd4640 /wd4619 /wd4350 /wd4351

src/blackmisc/aviation/aircraftengine.cpp

@@ -28,7 +28,7 @@ namespace BlackMisc
         {
             Q_UNUSED(i18n);
             QString s(m_number);
-            s += m_on;
+            s += BlackMisc::boolToOnOff(m_on);
             return s;
         }
     } // namespace