Prevent duplicate `map` sections in `renderd.conf` #1968

Job	Run time
freebsd14 (CMake) (LLVM)	7m 55s
debian:unstable (CMake) (GNU)	10s
macos-14 (Autotools) (LLVM)	5m 7s
fedora:rawhide (CMake) (GNU)	3m 23s
macos-14 (CMake) (LLVM)	9m 41s
ubuntu:devel (CMake) (GNU)	3m 21s
debian:12 (Latest Mapnik) (CMake) (GNU)	3m 36s
ubuntu:22.04 (Autotools) (GNU)	1m 56s
ubuntu:22.04 (Latest Mapnik) (CMake) (GNU)	3m 28s
ubuntu:22.04 (Autotools) (LLVM)	2m 33s
ubuntu:22.04 (CMake) (GNU)	4m 9s
ubuntu:22.04 (CMake) (LLVM)	3m 13s
	48m 32s

Provide feedback