dns-reports is reporting on devices with no interfaces

[acaronmd]

dns-reports checks for dns entries for devices with IPs assigned to an interface. This line filters out devices with no interfaces, but in my case, it still returns devices with no interfaces, because it returns an empty QuerySet
https://github.com/netbox-community/reports/blob/9b4a4fab71c5a10469988f362f410b295b9f317e/reports/ipam-reports/dns-reports.py#L13

I've fixed the issue locally by replacing it with this line.
if not device.interfaces.exists():

http://docs.djangoproject.com/en/dev/ref/models/querysets/#exists