Avoid double-query on csubs/casubs collections

There is a slight change in the logic on processSubscriptions() in MongoCommmonUpdate.cpp. Originally, the function early return in the first database error. Now, we pass for all the subscriptions, accumulating the errors in `err` in the case several ones occurs. This way, the processSubscriptions() in MongoCommmonUpdate.cpp behaves the same than in MongoCommmonRegister.cpp.