Fix for username = response[0]['dn'] KeyError

[netvoip]

Trying to test extension, not working out of the box as expected, got error when entering intentionally wrong credentials

flask_ldapconn\__init__.py", line 162, in authenticate
username = response[0]['dn']
KeyError: 'dn' 

Slight code changing required. In line 162 of __init__.py
except (LDAPInvalidDnError, LDAPInvalidFilterError, IndexError):
to empty
except:
gave correct error handling! Hope this will help to someone.