fix bug when we compute the mean of messages from skill to game
fix bug when we compute the mean of messages from skill to game

probml/pmtk3,probml/pmtk3,korkam/pmtk3,korkam/pmtk3,korkam/pmtk3,probml/pmtk3,probml/pmtk3,probml/pmtk3,korkam/pmtk3,korkam/pmtk3,korkam/pmtk3,probml/pmtk3