work-around race in Worker.working

From our Hoptoad:

NoMethodError: undefined method `job' for nil:NilClass
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/resque-1.5.0/lib/resque/server/views/working.erb:46:in `render_erb'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/resque-1.5.0/lib/resque/server/views/working.erb:70:in `sort_by'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/resque-1.5.0/lib/resque/server/views/working.erb:46:in `each'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/resque-1.5.0/lib/resque/server/views/working.erb:46:in `sort_by'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/resque-1.5.0/lib/resque/server/views/working.erb:46:in `render_erb'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/sinatra-0.9.4/lib/sinatra/base.rb:315:in `render_erb'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/sinatra-0.9.4/lib/sinatra/base.rb:265:in `__send__'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/sinatra-0.9.4/lib/sinatra/base.rb:265:in `render'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/sinatra-0.9.4/lib/sinatra/base.rb:228:in `erb'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/resque-1.5.0/lib/resque/server.rb:84:in `partial'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/resque-1.5.0/lib/resque/server/views/overview.erb:3:in `render_erb'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/sinatra-0.9.4/lib/sinatra/base.rb:315:in `render_erb'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/sinatra-0.9.4/lib/sinatra/base.rb:265:in `__send__'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/sinatra-0.9.4/lib/sinatra/base.rb:265:in `render'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/sinatra-0.9.4/lib/sinatra/base.rb:228:in `erb'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/resque-1.5.0/lib/resque/server.rb:102:in `show'
/data/awsm/releases/20100406054950/gems/ruby/1.8/gems/resque-1.5.0/lib/resque/server.rb:127:in `GET /overview.poll'

lib/resque/worker.rb

@@ -35,7 +35,7 @@ def self.working
       names.map! { |name| "worker:#{name}" }
       redis.mapped_mget(*names).keys.map do |key|
         find key.sub("worker:", '')
-      end
+      end.compact
     end
 
     # Returns a single worker object. Accepts a string id.