Return zero results when no valid coords given.

Fixes issue #75 (ActiveRecord) and more (Mongoid).

lib/geocoder/stores/active_record.rb

@@ -36,7 +36,7 @@ module Geocoder::Store
           if latitude and longitude
             near_scope_options(latitude, longitude, *args)
           else
-            {}
+            where(:id => false) # no results if no lat/lon given
           end
         }
       end

lib/geocoder/stores/mongoid.rb

@@ -17,6 +17,10 @@ module Geocoder::Store
 
         scope :near, lambda{ |location, *args|
           coords  = Geocoder::Calculations.extract_coordinates(location)
+
+          # no results if no lat/lon given
+          return criteria.where(:id => false) unless coords.is_a?(Array)
+
           radius  = args.size > 0 ? args.shift : 20
           options = args.size > 0 ? args.shift : {}