Fix group_digits for negative integers #5916

Job	Run time
mingw (mingw64)	5m 3s
build (windows-2019, Win32, v142, 17, Debug)	1m 19s
mingw (ucrt64)	5m 1s
build (windows-2019, Win32, v142, 17, Release)	2m 30s
build (windows-2019, Win32, v142, 17, -DBUILD_SHARED_LIBS=ON, Debug)	2m 12s
build (windows-2019, Win32, v142, 17, -DBUILD_SHARED_LIBS=ON, Release)	1m 58s
build (windows-2019, x64, v140, 14, Debug)	1m 31s
build (windows-2019, x64, v140, 14, Release)	2m 11s
build (windows-2019, x64, v141, 17, Debug)	2m 11s
build (windows-2019, x64, v141, 17, Release)	2m 40s
build (windows-2019, x64, v142, 17, Debug)	1m 34s
build (windows-2019, x64, v142, 17, Release)	2m 34s
build (windows-2019, x64, v142, 17, -DBUILD_SHARED_LIBS=ON, Debug)	2m 6s
build (windows-2019, x64, v142, 17, -DBUILD_SHARED_LIBS=ON, Release)	2m 30s
build (windows-2019, x64, v142, 20, Debug)	2m 54s
build (windows-2019, x64, v142, 20, Release)	3m 11s
build (windows-2022, x64, v143, Debug, 20)	1m 55s
	43m 20s

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