Fix edge case in tcod.noise.grid #986

Job	Run time
mypy	23s
ruff	7s
sdist	43s
tox (ubuntu-latest)	1m 43s
tox (windows-latest)	2m 11s
test-docs	1m 33s
parse_sdl (windows-latest, 2.0.14)	40s
parse_sdl (windows-latest, 2.0.16)	33s
parse_sdl (macos-latest, 2.0.14)	21s
parse_sdl (macos-latest, 2.0.16)	20s
build (ubuntu-latest, 3.8, x64)	3m 5s
build (ubuntu-latest, pypy-3.8, x64)	3m 4s
parse_sdl (windows-latest, 2.30.0)	43s
linux-wheels (x86_64, cp38-manylinux*)	1m 50s
build (windows-latest, pypy-3.8, x86)	4m 16s
build-macos (cp38-*_universal2)	4m 56s
build (windows-latest, 3.8, x86)	3m 49s
build (windows-latest, pypy-3.8, x64)	4m 4s
linux-wheels (x86_64, pp38-manylinux*)	1m 57s
build (windows-latest, 3.8, x64)	3m 17s
linux-wheels (aarch64, cp38-manylinux*)	12m 35s
linux-wheels (aarch64, pp38-manylinux*)	11m 40s
build-macos (pp38-*)	3m 45s
parse_sdl (macos-latest, 2.30.0)	18s
publish	0s
	1h 7m 53s

Provide feedback