RoboRumble ranking unstable

For unknown reason, the RoboRumble ranking has lost a lot of pairings. MiniRumble and smaller seem not effected. So it will take a while for it to stabelize as there are lots of bots that are missing 1-40 pairings.

That may be caused by a design flaw of the rumble client, which I didn't verify though. If the rumble cannot read robowiki's participants list, it will load a local cache instead. However, if that cache is outdated, it may cause the rumble to loose pairings, and recovering takes much longer. But this seems not to be the case losing 40 pairings.

Another possibility may be that the rumble client got a truncated participant list due to network issues, for this case, I may modify the client to check some flag to make sure the loaded participants list is full.