if distribution does not exists in other mirror, it breaks the links

[jeremy-clerc]

For example, distribution is in integration mirror but not production mirror.

Looking for distribution in integration is ok, then clicking in the top menu on production mirror show not found which is normal. The problem is if now I want to go back to the integration mirror by clicking on integration (in the top menu), the link is: http://thispan/mirror/integration/no_such_distribution. I think it should be http://thispan/mirror/integration/distribution/File-Stat if we do not want something complicated and say we do not know yet if this module exists in integration.