Fix typo in `mod_tile.c` #728

Job	Run time
FreeBSD-14.1-STABLE (CMake) (LLVM)	2m 5s
debian:12 (Latest Mapnik) (CMake) (GNU)	15m 13s
macos-15 (CMake) (LLVM)	6m 8s
ubuntu:24.04 (Latest Mapnik) (CMake) (GNU)	13m 35s
debian:unstable (CMake) (GNU)	3m 22s
fedora:rawhide (CMake) (GNU)	3m 11s
ubuntu:devel (CMake) (GNU)	3m 25s
ubuntu:24.04 (Autotools) (GNU)	2m 23s
ubuntu:24.04 (Autotools) (LLVM)	2m 18s
ubuntu:24.04 (CMake) (GNU)	3m 21s
ubuntu:24.04 (CMake) (LLVM)	3m 15s
	58m 16s

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