fix zero bin in categorical split

[guolinke]

to fix #3273

[guolinke]

@jameslamb
any ideas about /Users/runner/work/LightGBM/LightGBM/lightgbm.Rcheck/00_pkg_src/lightgbm/src/src/lightgbm_R.cpp:679:41: warning: cast between incompatible function types from 'LGBM_SER* (*)(LGBM_SE, LGBM_SE, LGBM_SE)' {aka 'LGBM_SER* (*)(LGBM_SER*, LGBM_SER*, LGBM_SER*)'} to 'DL_FUNC' {aka 'void* (*)()'} [-Wcast-function-type] ?

[jameslamb]

I think it can safely be ignored, and would be fixed by #3016.

The failing checks in this PR are because of this

* checking installed package size ... NOTE
  installed size is  5.2Mb
  sub-directories of 1Mb or more:
    libs   4.5Mb

I think it is ok to ignore that NOTE, and that can be done by increasing the limit here:

LightGBM/.ci/test_r_package.sh

Lines 202 to 206 in 69a2691

	if [[ $OS_NAME == "linux" ]] && [[ $R_BUILD_TYPE == "cran" ]]; then
	ALLOWED_CHECK_NOTES=2
	else
	ALLOWED_CHECK_NOTES=1
	fi

. Since we had this problem in another PR too (#3264 (comment)), I'll just make that change right now in a separate PR. Otherwise we will keep hitting this into one of these is merged.

[github-actions]

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