Update active_record instantiated_hash to default to {} instead of nil

I started getting this on image requests where ActiveRecord is not loaded.

NoMethodError (undefined method sort' for nil:NilClass):
oink (0.10.0) lib/oink/utils/hash_utils.rb:5:into_sorted_array'
oink (0.10.0) lib/oink/middleware.rb:48:in log_activerecord'
oink (0.10.0) lib/oink/middleware.rb:21:incall'
warden (1.2.1) lib/warden/manager.rb:35:in block in call'
warden (1.2.1) lib/warden/manager.rb:34:incatch'
warden (1.2.1) lib/warden/manager.rb:34:in call'
actionpack (3.2.1) lib/action_dispatch/middleware/best_standards_support.rb:17:incall'
rack (1.4.1) lib/rack/etag.rb:23:in call'
rack (1.4.1) lib/rack/conditionalget.rb:25:incall'
actionpack (3.2.1) lib/action_dispatch/middleware/head.rb:14:in call'
remotipart (1.0.2) lib/remotipart/middleware.rb:30:incall'
actionpack (3.2.1) lib/action_dispatch/middleware/params_parser.rb:21:in call'
actionpack (3.2.1) lib/action_dispatch/middleware/flash.rb:242:incall'
rack (1.4.1) lib/rack/session/abstract/id.rb:205:in context'
rack (1.4.1) lib/rack/session/abstract/id.rb:200:incall'
rack-p3p (0.5.0) lib/rack-p3p.rb:11:in call'
actionpack (3.2.1) lib/action_dispatch/middleware/cookies.rb:338:incall'
activerecord (3.2.1) lib/active_record/query_cache.rb:64:in call'
activerecord (3.2.1) lib/active_record/connection_adapters/abstract/connection_pool.rb:443:incall'
actionpack (3.2.1) lib/action_dispatch/middleware/callbacks.rb:28:in block in call'
activesupport (3.2.1) lib/active_support/callbacks.rb:405:in_run__4079966539919658034__call__3128255809264830011__callbacks'
activesupport (3.2.1) lib/active_support/callbacks.rb:405:in __run_callback'
activesupport (3.2.1) lib/active_support/callbacks.rb:385:in_run_call_callbacks'
activesupport (3.2.1) lib/active_support/callbacks.rb:81:in run_callbacks'
actionpack (3.2.1) lib/action_dispatch/middleware/callbacks.rb:27:incall'
actionpack (3.2.1) lib/action_dispatch/middleware/reloader.rb:65:in call'
actionpack (3.2.1) lib/action_dispatch/middleware/remote_ip.rb:31:incall'
actionpack (3.2.1) lib/action_dispatch/middleware/debug_exceptions.rb:16:in call'
actionpack (3.2.1) lib/action_dispatch/middleware/show_exceptions.rb:56:incall'
railties (3.2.1) lib/rails/rack/logger.rb:26:in call_app'
railties (3.2.1) lib/rails/rack/logger.rb:16:incall'
actionpack (3.2.1) lib/action_dispatch/middleware/request_id.rb:22:in call'
rack (1.4.1) lib/rack/methodoverride.rb:21:incall'
rack (1.4.1) lib/rack/runtime.rb:17:in call'
activesupport (3.2.1) lib/active_support/cache/strategy/local_cache.rb:72:incall'
rack (1.4.1) lib/rack/lock.rb:15:in call'
railties (3.2.1) lib/rails/engine.rb:479:incall'
railties (3.2.1) lib/rails/application.rb:220:in call'
railties (3.2.1) lib/rails/railtie/configurable.rb:30:inmethod_missing'
rack (1.4.1) lib/rack/deflater.rb:13:in call'
rack (1.4.1) lib/rack/content_length.rb:14:incall'
railties (3.2.1) lib/rails/rack/log_tailer.rb:14:in call'
rack (1.4.1) lib/rack/handler/webrick.rb:59:inservice'
/Users/gabe/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/webrick/httpserver.rb:138:in service'
/Users/gabe/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/webrick/httpserver.rb:94:inrun'
/Users/gabe/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'