AirspaceManager: Remove pointer check before delete

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

src/AirspaceManagement/AirspaceManager.cc

@@ -48,21 +48,16 @@ AirspaceManager::AirspaceManager(QGCApplication* app, QGCToolbox* toolbox)
 //-----------------------------------------------------------------------------
 AirspaceManager::~AirspaceManager()
 {
-    if(_advisories) {
     delete _advisories;
-    }
-    if(_weatherProvider) {
+    _advisories = nullptr;
     delete _weatherProvider;
-    }
-    if(_ruleSetsProvider) {
+    _weatherProvider = nullptr;
     delete _ruleSetsProvider;
-    }
-    if(_airspaces) {
+    _ruleSetsProvider = nullptr;
     delete _airspaces;
-    }
-    if(_flightPlan) {
+    _airspaces = nullptr;
     delete _flightPlan;
-    }
+    _flightPlan = nullptr;
 }
 
 //-----------------------------------------------------------------------------