[ObjDet] Improve handling of label files
[ObjDet] Improve handling of label files

Specifically, empty or invalid files

bygreencn/DIGITS,gheinrich/DIGITS-GAN,ethantang95/DIGITS-GAN,TimZaman/DIGITS,ethantang95/DIGITS-GAN,Deepomatic/DIGITS,gheinrich/DIGITS-GAN,TimZaman/DIGITS,bygreencn/DIGITS,ethantang95/DIGITS,ethantang95/DIGITS,ethantang95/DIGITS-GAN,Deepomatic/DIGITS,TimZaman/DIGITS,ethantang95/DIGITS-GAN,Deepomatic/DIGITS,ethantang95/DIGITS,Deepomatic/DIGITS,TimZaman/DIGITS,bygreencn/DIGITS,gheinrich/DIGITS-GAN,bygreencn/DIGITS,gheinrich/DIGITS-GAN,ethantang95/DIGITS