shell vulnerabilities fixed

[kbhujbal]

1. Replaced subprocess.Popen("mkdir -p "+output_folder, shell=True) with Path(output_folder).mkdir(parents=True, exist_ok=True)
   This fixes a shell injection risk where malicious folder names could run arbitrary commands

2. Fixed main() function - it was trying to unpack 1 value into 4 variables, now it loops through folders correctly