Fix edge case in tcod.noise.grid #985

Job	Run time
ruff	5s
mypy	21s
sdist	38s
tox (ubuntu-latest)	1m 44s
tox (windows-latest)	1m 53s
parse_sdl (macos-latest, 2.0.14)	22s
parse_sdl (windows-latest, 2.0.16)	46s
parse_sdl (macos-latest, 2.30.0)	21s
parse_sdl (macos-latest, 2.0.16)	22s
parse_sdl (windows-latest, 2.30.0)	44s
parse_sdl (windows-latest, 2.0.14)	45s
build (windows-latest, 3.8, x64)	3m 13s
build (ubuntu-latest, 3.8, x64)	3m 11s
build (windows-latest, pypy-3.8, x86)	4m 46s
build (windows-latest, 3.8, x86)	4m 18s
build (windows-latest, pypy-3.8, x64)	5m 0s
build (ubuntu-latest, pypy-3.8, x64)	3m 6s
build-macos (cp38-*_universal2)	5m 31s
test-docs	1m 37s
build-macos (pp38-*)	3m 47s
linux-wheels (x86_64, cp38-manylinux*)	1m 55s
linux-wheels (x86_64, pp38-manylinux*)	2m 10s
linux-wheels (aarch64, cp38-manylinux*)	12m 26s
linux-wheels (aarch64, pp38-manylinux*)	11m 22s
publish	0s
	1h 10m 23s

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