Fix a problem with initialisation sequence (Fix #3550)

- for auto-location from Network at startup,
  we cannot use LandscapeMgr to set ZeroColor landscape
  as it was not yet initialized.
- Added a late initialisation of that in StelApp. Not pretty,
  but I don't see another place for this.

src/core/StelApp.cpp

@@ -588,6 +588,14 @@ void StelApp::init(QSettings* conf)
 	LandscapeMgr* landscape = new LandscapeMgr();
 	landscape->init();
 	getModuleMgr().registerModule(landscape);
+	// Only now we can switch to auto-landscape. (GH:#3550)
+	if (landscape->getFlagLandscapeAutoSelection() && (confSettings->value("init_location/location", "auto").toString() == "auto"))
+	{
+		StelLocation loc=core->getCurrentLocation();
+		QColor color=planetLocationMgr->getColorForCoordinates(loc.getLongitude(), loc.getLatitude());
+		QString landscapeAutoName=QString("ZeroColor(%1)").arg(Vec3f(color).toStr());
+		emit core->targetLocationChanged(loc, landscapeAutoName); // inform others about our next location. E.g., let LandscapeMgr load a new landscape.
+	}
 
 	SplashScreen::showMessage(q_("Initializing grid lines..."));
 	GridLinesMgr* gridLines = new GridLinesMgr();

src/core/StelLocationMgr.cpp

@@ -1171,9 +1171,9 @@ void StelLocationMgr::changeLocationFromNetworkLookup()
 			// Ensure that ipTimeZone is a valid IANA timezone name!
 			QTimeZone ipTZ(ipTimeZone.toUtf8());
 			core->setCurrentTimeZone( !ipTZ.isValid() || ipTimeZone.isEmpty() ? "LMST" : ipTimeZone);
-			LandscapeMgr *lMgr=GETSTELMODULE(LandscapeMgr);
+			LandscapeMgr *lMgr=GETSTELMODULE_SILENT(LandscapeMgr); // This may fail during StelApp:init() (GH:#3550)
 			QString landscapeAutoName;
-			if (lMgr->getFlagLandscapeAutoSelection())
+			if (lMgr && lMgr->getFlagLandscapeAutoSelection())
 			{
 				QColor color=getColorForCoordinates(loc.getLongitude(), loc.getLatitude());
 				landscapeAutoName=QString("ZeroColor(%1)").arg(Vec3f(color).toStr());