bug fix in get_group
bug fix in get_group

Laurae2/LightGBM,huanzhang12/LightGBM,sightmachine/LightGBM,wxchan/LightGBM,Laurae2/LightGBM,wxchan/LightGBM,fstonezst/LightGBM,fstonezst/LightGBM,cbecker/LightGBM,microsoft/LightGBM,henry0312/LightGBM,olofer/LightGBM,microsoft/LightGBM,wxchan/LightGBM,wxchan/LightGBM,fstonezst/LightGBM,henry0312/LightGBM,sightmachine/LightGBM,olofer/LightGBM,huanzhang12/lightgbm-gpu,Laurae2/LightGBM,huanzhang12/LightGBM,huanzhang12/LightGBM,wxchan/LightGBM,fstonezst/LightGBM,Laurae2/LightGBM,huanzhang12/lightgbm-gpu,microsoft/LightGBM,henry0312/LightGBM,Allardvm/LightGBM,cbecker/LightGBM,henry0312/LightGBM,fstonezst/LightGBM,Allardvm/LightGBM,microsoft/LightGBM,Allardvm/LightGBM,Allardvm/LightGBM,sightmachine/LightGBM,henry0312/LightGBM,cbecker/LightGBM,cbecker/LightGBM,olofer/LightGBM,sightmachine/LightGBM,huanzhang12/LightGBM,Laurae2/LightGBM,huanzhang12/lightgbm-gpu,microsoft/LightGBM,huanzhang12/lightgbm-gpu,Allardvm/LightGBM,olofer/LightGBM,olofer/LightGBM,huanzhang12/LightGBM,huanzhang12/lightgbm-gpu