Add a check for itb review file

[evelyn-schmidt]

https://github.com/griffithlab/neoag_vaccine_scripts/blob/a856712861ae3af9a5b68976078942bb7253022f/scripts/generate_reviews_files.py#L75C1-L77C102

Sometimes this first line has already been removed, add a check so these lines are only executed if the blank line exists