Fix error when casting blank literal score as int for ongoing game

[AndrewYinLi]

I fixed the error in which I could not call box_score() during the top of an inning for an ongoing game. box_score() would result in throwing an error because __init__ did not account for the score string for the top of an inning being a blank literal i.e. '' and would attempt to cast '' as an int. I also got rid of the try and except because it felt hacky and instead I check to see whether the score string returns true when isdigit() is called before deciding whether or not to cast the score string as an int.

Related issue that I opened: #127