[Backport] Fix typo in mod_tile.c (#474) #730

Job	Run time
FreeBSD-14.1-STABLE (CMake) (LLVM)	1m 28s
debian:unstable (CMake) (GNU)	1m 56s
debian:12 (Latest Mapnik) (CMake) (GNU)	13m 46s
fedora:rawhide (CMake) (GNU)	1m 52s
macos-15 (CMake) (LLVM)	4m 50s
ubuntu:24.04 (Latest Mapnik) (CMake) (GNU)	13m 0s
ubuntu:devel (CMake) (GNU)	2m 6s
ubuntu:24.04 (Autotools) (GNU)	2m 18s
ubuntu:24.04 (Autotools) (LLVM)	2m 30s
ubuntu:24.04 (CMake) (GNU)	2m 17s
ubuntu:24.04 (CMake) (LLVM)	3m 27s
	49m 30s

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