Fix Redis::ServerError on Apisonator

From Bugsnag:

https://app.bugsnag.com/3scale-networks-sl/backend/errors/60ee140869f8ae00071c23ac?filters[error.status]=open&filters[event.since]=30d&filters[app.release_stage]=production

Protocol::Redis::ServerError
ERR value is not an integer or out of range
 

1. Worker
2. ReporJob
3. Aggregate
4. lib/3scale/backend/storage_async/async_redis.rb:25 block (2 levels) in call_pipeline

res = commands.size.times.map do
begin
  connection.read_response
rescue ::Protocol::Redis::ServerError => e
  first_err ||= e
  nil