Add a convenience function to check if model owns any object

GUI/ba3d/ba3d/model/model.cpp

@@ -144,6 +144,14 @@ void Model::releaseGeometries()
         o->releaseGeometry();
 }
 
+bool Model::modelIsEmpty()
+{
+    if(objects.isEmpty() && objectsBlend.isEmpty())
+        return true;
+    else
+        return false;
+}
+
 void Model::draw(Canvas& canvas) const
 {
     for (auto o : objects)

GUI/ba3d/ba3d/model/model.h

@@ -46,6 +46,8 @@ public:
 
     void releaseGeometries(); // may be called any time
 
+    bool modelIsEmpty();
+
     virtual void cameraUpdated(Camera const&) {}
 
     Camera::Position defCamPos;    // default camera params