Remove path.isfile check

[paivao]

On the line below: https://github.com/Busindre/dumpzilla/blob/ec337da722441c7480f280b14c273718fabc6c96/dumpzilla.py#L141

you can see that is a check if the libnss_path var is a vaid file, what is always False.

Since CDLL call with handle this correctly, I can assume this is redundant and causes false-negatives.