Fix of several issues related to gizmos updating and undo/redo

Common gizmos data cannot be used in on_set_state method
Also prevented calling render on empty GLVertexArrays

src/slic3r/GUI/Gizmos/GLGizmoFlatten.cpp

@@ -28,8 +28,7 @@ bool GLGizmoFlatten::on_init()
 
 void GLGizmoFlatten::on_set_state()
 {
-    if (m_state == On && is_plane_update_necessary())
-        update_planes();
+
 }
 
 CommonGizmosDataID GLGizmoFlatten::on_get_requirements() const
@@ -81,7 +80,8 @@ void GLGizmoFlatten::on_render() const
             else
                 glsafe(::glColor4f(0.9f, 0.9f, 0.9f, 0.5f));
 
-            m_planes[i].vbo.render();
+            if (m_planes[i].vbo.has_VBOs())
+                m_planes[i].vbo.render();
         }
         glsafe(::glPopMatrix());
     }