Allow for bounds to be nil or already flattened

lib/geocoder/stores/active_record.rb

@@ -48,9 +48,8 @@ module Geocoder::Store
         # (<tt>[[sw_lat, sw_lon], [ne_lat, ne_lon]]</tt>).
         #
         scope :within_bounding_box, lambda{ |bounds|
-          sw_lat, sw_lng, ne_lat, ne_lng = bounds.flatten!
+          sw_lat, sw_lng, ne_lat, ne_lng = bounds.flatten if bounds
           return where(:id => false) unless sw_lat && sw_lng && ne_lat && ne_lng
-
           spans = "latitude BETWEEN #{sw_lat} AND #{ne_lat} AND "
           spans << if sw_lng > ne_lng   # Handle a box that spans 180
             "longitude BETWEEN #{sw_lng} AND 180 OR longitude BETWEEN #{ne_lng} and -180"