Add a check for the recently added routines to combine crc32 checksums. This
change adds more code coverage, however the checksum_fuzzer still does not pass
the complexity check: (the threshold is at 100)
oss-fuzz$ build/out/zlib/checksum_fuzzer -runs=10 2>&1 | grep -Po "INFO: Loaded [[:digit:]]+ module.*\(.*(counters|guards)\):[[:space:]]+\K[[:digit:]]+"
92