Fix crash when not setting any regions on distrib model
Fix crash when not setting any regions on distrib model

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