fixed a minor error in 'window-fast' normalization method that came up during testing
fixed a minor error in 'window-fast' normalization method that came up during testing

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