check for availability of vtkMapServerSource before using it
check for availability of vtkMapServerSource before using it

when USE_DRC_MAPS is disabled then this class is not built

openhumanoids/oh-distro,openhumanoids/oh-distro,openhumanoids/oh-distro,openhumanoids/oh-distro,openhumanoids/oh-distro,openhumanoids/oh-distro,openhumanoids/oh-distro,openhumanoids/oh-distro