Fix bugs that occur with AD removal of user on at least on Python 3.8+ maybe lower

[jeremybusk]

• Fix error after deleted synced user from AD group and resync so script doesn't error out
• Rewrite list comprehensions for readability and not get self missing due to self not being in LC scope (I was doing pdb.set_trace()
• Fix bug on return value by adding None
• Defined type on ldap_users so it doesn't error when is an emptyset

These are the best without doing major rewrite but it will at least allow the script to work Tested on Ubuntu 20.04 Python3.8 using Python -m venv

[scoopex]

Many thanks.