Fix handling of non-subclassed Person.for_location
Fix handling of non-subclassed Person.for_location

Person.criteria_for_types_for_location was breaking on nil _type
value. Since plain Person objects (i.e. Twitter ingested) don't have
reliable location data, return scope that has no effect.

Supports #237

opengovernment/askthem,mapineda/askthem,opengovernment/askthem,mapineda/askthem,mapineda/askthem,opengovernment/askthem,mapineda/askthem,opengovernment/askthem