fix missing return in RaycastVolumeRenderer::renderFrame()
fix missing return in RaycastVolumeRenderer::renderFrame()

MengjiaoH/ospray,wilsonCernWq/ospray,ospray/OSPRay,wilsonCernWq/ospray,ospray/OSPRay,ospray/OSPRay,MengjiaoH/ospray,ospray/OSPRay,MengjiaoH/ospray,wilsonCernWq/ospray,MengjiaoH/ospray,MengjiaoH/ospray