fix for case where tif image directory has no data in offsets
fix for case where tif image directory has no data in offsets

kunallillaney/thunder,oliverhuangchao/thunder,zhwa/thunder,kcompher/thunder,thunder-project/thunder,mikarubi/thunder,j-friedrich/thunder,mikarubi/thunder,jwittenbach/thunder,kcompher/thunder,poolio/thunder,zhwa/thunder,kunallillaney/thunder,j-friedrich/thunder,broxtronix/thunder,pearsonlab/thunder,broxtronix/thunder,poolio/thunder,oliverhuangchao/thunder,pearsonlab/thunder