Several gcc and clang fixes

This superseeds also f1199793 by a cleaner workaround.

src/blackgui/components/remoteaircraftselector.cpp

@@ -33,7 +33,7 @@ namespace BlackGui
 
         BlackMisc::Aviation::CCallsign CRemoteAircraftSelector::getSelectedCallsign() const
         {
-            const CCallsign empty;
+            const CCallsign empty {};
             int index = ui->cb_RemoteAircraftSelector->currentIndex();
             if (index < 0 || index > this->m_aircraft.size()) { return empty; }
             return m_aircraft[index].getCallsign();

src/blackmisc/aviation/aircraftengine.h

@@ -24,7 +24,7 @@ namespace BlackMisc
         public:
 
             //! Default constructor
-            CAircraftEngine() = default;
+            CAircraftEngine() {}
 
             //! Constructor
             CAircraftEngine(int number, bool on);

src/blackmisc/aviation/aircraftenginelist.cpp

@@ -30,23 +30,7 @@ namespace BlackMisc
         CAircraftEngine CAircraftEngineList::getEngine(int engineNumber) const
         {
             Q_ASSERT(engineNumber >= 0);
-
+            return this->findBy(&CAircraftEngine::getNumber, engineNumber).frontOrDefault();
-            // The following commented line results in a gcc compiler segfault:
-            //
-            // internal compiler error: in size_binop_loc, at fold-const.c:1450
-            // } // namespace
-            // ^
-            //
-            // frontOrDefault() is defined as:
-            // static const value_type def; return empty() ? def : front();
-            // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-            // Workaround it by using non static const value instead.
-
-            //return this->findBy(&CAircraftEngine::getNumber, engineNumber).frontOrDefault();
-
-            const CAircraftEngine def;
-            auto results = this->findBy(&CAircraftEngine::getNumber, engineNumber);
-            return results.empty() ? def : front();
         }
 
         bool CAircraftEngineList::isEngineOn(int engineNumber) const

src/blackmisc/sequence.h

@@ -165,7 +165,7 @@ namespace BlackMisc
         /*!
          * \brief Access the first element, or a default-initialized value if the sequence is empty.
          */
-        const_reference frontOrDefault() const { static const value_type def; return empty() ? def : front(); }
+        const_reference frontOrDefault() const { static const value_type def {}; return empty() ? def : front(); }
 
         /*!
          * \brief Access the first element, or a default-initialized value if the sequence is empty.