20240814 fix strat split

[buffalotheory]

Running coco_data_split.py with the --how='stratified' option resulted in a ZeroDivisionError exception. This pull request is a proposed fix.

python3 coco_data_split.py --how='stratified' --data_path=../dataset/netcdf --coco_path=./coco_files/ --prefix=stratified_30 --num_patches=30 --seed=16
Traceback (most recent call last):
  File "/Users/iahansen/admin/master_study/P7/repo/Sen4AgriNet/s4am2/coco_data_split.py", line 200, in <module>
    new_train_r = (args.num_patches * train_r) / all_patches
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~
ZeroDivisionError: division by zero