mainapplication: fix destruction ordering

Every models (like UtilsAdapter for example) owns a pointer of
LRCInstance. So, when the MainApplication is destroyed, the QmlEngine
and all structures owning a pointer of LRCInstance MUST be destroyed
before LRCInstance to avoid any segfault

GitLab: #631
Change-Id: Id30aaca325fe7172188bba468acd73525e62a34a

src/mainapplication.cpp

@@ -155,7 +155,11 @@ MainApplication::MainApplication(int& argc, char** argv)
     QObject::connect(this, &QApplication::aboutToQuit, [this] { cleanup(); });
 }
 
-MainApplication::~MainApplication() {}
+MainApplication::~MainApplication()
+{
+    engine_.reset();
+    lrcInstance_.reset();
+}
 
 bool
 MainApplication::init()

src/mainapplication.h

@@ -80,7 +80,6 @@ private:
 private:
     QScopedPointer<QFile> debugFile_;
     QScopedPointer<QQmlApplicationEngine> engine_;
-
     QScopedPointer<LRCInstance> lrcInstance_;
 
     QScopedPointer<ConnectivityMonitor> connectivityMonitor_;