FIX: never return empty prop (always set m_Prop3D to m_Actor). Before: when invisible when OpenGLRenderer::UpdateIncludingVtkActors was called, prop was NULL, thus not added to prop-list in vtkRenderer and stayed invisible after switching to visible, until some called UpdateIncludinVtkActors again.
FIX: never return empty prop (always set m_Prop3D to m_Actor). Before: when invisible when OpenGLRenderer::UpdateIncludingVtkActors was called, prop was NULL, thus not added to prop-list in vtkRenderer and stayed invisible after switching to visible, until some called UpdateIncludinVtkActors again.



rfloca/MITK,iwegner/MITK,iwegner/MITK,lsanzdiaz/MITK-BiiG,lsanzdiaz/MITK-BiiG,MITK/MITK,RabadanLab/MITKats,lsanzdiaz/MITK-BiiG,fmilano/mitk,rfloca/MITK,fmilano/mitk,fmilano/mitk,rfloca/MITK,lsanzdiaz/MITK-BiiG,rfloca/MITK,RabadanLab/MITKats,NifTK/MITK,lsanzdiaz/MITK-BiiG,danielknorr/MITK,nocnokneo/MITK,rfloca/MITK,iwegner/MITK,nocnokneo/MITK,MITK/MITK,nocnokneo/MITK,RabadanLab/MITKats,rfloca/MITK,danielknorr/MITK,nocnokneo/MITK,danielknorr/MITK,nocnokneo/MITK,RabadanLab/MITKats,fmilano/mitk,MITK/MITK,fmilano/mitk,MITK/MITK,nocnokneo/MITK,iwegner/MITK,fmilano/mitk,danielknorr/MITK,fmilano/mitk,nocnokneo/MITK,danielknorr/MITK,NifTK/MITK,iwegner/MITK,NifTK/MITK,MITK/MITK,RabadanLab/MITKats,danielknorr/MITK,lsanzdiaz/MITK-BiiG,rfloca/MITK,danielknorr/MITK,lsanzdiaz/MITK-BiiG,NifTK/MITK,MITK/MITK,NifTK/MITK,iwegner/MITK,NifTK/MITK,RabadanLab/MITKats,lsanzdiaz/MITK-BiiG