fall back to blocking behavior for em_mysql2 AR adapter if EM isn't running

lib/active_record/connection_adapters/em_mysql2_adapter.rb

@@ -42,6 +42,7 @@ module Mysql2
       end
 
       def query(sql, opts={})
+        if EM.reactor_running?
           super(sql, opts.merge(:async => true))
           deferable = ::EM::DefaultDeferrable.new
           ::EM.watch(self.socket, Watcher, self, deferable).notify_readable = true
@@ -53,6 +54,9 @@ module Mysql2
             fiber.resume(err)
           end
           Fiber.yield
+        else
+          super(sql, opts)
+        end
       end
     end
   end