added error-catchers when trying to map/unmap a 'none'-format frame buffer
added error-catchers when trying to map/unmap a 'none'-format frame buffer

wilsonCernWq/ospray,wilsonCernWq/ospray,favreau/OSPRay,wilsonCernWq/ospray,ospray/OSPRay,ospray/OSPRay,Twinklebear/OSPRay,favreau/OSPRay,Twinklebear/OSPRay,favreau/OSPRay,MengjiaoH/ospray,MengjiaoH/ospray,Twinklebear/OSPRay,favreau/OSPRay,ospray/OSPRay,MengjiaoH/ospray,ospray/OSPRay,MengjiaoH/ospray,Twinklebear/OSPRay,MengjiaoH/ospray