fix warnings in debug mode about that not all control paths return a value (#2866)
fix warnings in debug mode about that not all control paths return a value (#2866)


henry0312/LightGBM,microsoft/LightGBM,henry0312/LightGBM,microsoft/LightGBM,henry0312/LightGBM,microsoft/LightGBM,microsoft/LightGBM,microsoft/LightGBM,henry0312/LightGBM,henry0312/LightGBM