[FIX] prevent type error when remote_addr is None

Fixes #740
Fixes #756

`self.geo_ip_resolver.record_by_addr` fails when `request.httprequest.remote_addr` returns None

Patch will give empty string instead of None. `self.geo_ip_resolver.record_by_addr` will then output None, which is the case 6ba14b38 tried to fix.