Fix signed integer overflow. #162

Job	Run time
build (ubuntu-latest, Debug, address)	21s
build (ubuntu-latest, Debug, memory)	25s
build (ubuntu-latest, Debug, undefined)	28s
build (ubuntu-latest, RelWithDebInfo, address)	30s
build (ubuntu-latest, RelWithDebInfo, memory)	41s
build (ubuntu-latest, RelWithDebInfo, undefined)	37s
build (ubuntu-latest, MinSizeRel, address)	28s
build (ubuntu-latest, MinSizeRel, memory)	31s
build (ubuntu-latest, MinSizeRel, undefined)	39s
build (ubuntu-latest, Release, address)	29s
build (ubuntu-latest, Release, memory)	40s
build (ubuntu-latest, Release, undefined)	39s
build (macOS-latest, Debug, address)	15s
build (macOS-latest, Debug, undefined)	12s
build (macOS-latest, RelWithDebInfo, address)	17s
build (macOS-latest, RelWithDebInfo, undefined)	21s
build (macOS-latest, MinSizeRel, address)	16s
build (macOS-latest, MinSizeRel, undefined)	23s
build (macOS-latest, Release, address)	18s
build (macOS-latest, Release, undefined)	18s
	8m 48s

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