Unstable behavior when running multiple rounds with -g option

Dear developers

Thank you for providing this useful tool.

I'm reporting an unstable behavior of APE-gen when running multiple rounds with -g option.
It happens in the rounds except for the first round that the process stops without error message and exiting, thus, stays running forever but gives no progress.
This behavior is somehow random, as I repeated the command below 10 times with exactly same configurations(same peptide, allele, and other options) and 7 out of 10 runs couldn't finish all rounds.
This behavior is the same whichever I add -b option or not.

`python APE_Gen.py -n 32 -l 100 -g 5 SVIKISVEPV HLA-A*02:01`

The point the process stops is always after the message 'Organizing RCD results' after which a progress bar usually shows up but doesn't in unlucky case.
Actually, 2 out of the 7 failure cases stopped at different point and exited with the error messages like:

> Organizing RCD results
> Progress: |**************************************************| 100.0% Complete
> -15.4834671
>
> Loading sampled conformations
> Num full confs: 30
> Saving filtered peptide confs
> Average filtered energy: -13.973028735714289
> Num filtered confs: 14
> Average filtered energy: -13.973028735714289
> Saving complete peptide-HLA complexes
> Traceback (most recent call last):
> File "APE_Gen.py", line 886, in
> main(sys.argv[1:])
> File "APE_Gen.py", line 505, in main
> folder_names = [str(s[0]) for s in array_splits]
> File "APE_Gen.py", line 505, in
> folder_names = [str(s[0]) for s in array_splits]
> IndexError: index 0 is out of bounds for axis 0 with size 0

Because the first round always successfully finishes, I can repeat multiple times with '-g 1', but then this is meaningless especially when I want to try -b option.

I appreciate if you investigate this behavior.