Fix potential DoS issue with p2c header #52

Job	Run time
osx (gcc)	8m 28s
linux (gcc, fedora:latest, true)	1m 27s
osx (clang)	8m 46s
linux (gcc, quay.io/centos/centos:stream9, true)	1m 26s
linux (gcc, quay.io/centos/centos:stream8, true)	1m 17s
linux (gcc, debian:testing, true)	3m 28s
linux (gcc, debian:latest, true)	3m 20s
linux (gcc, ubuntu:rolling, true)	2m 47s
linux (gcc, ubuntu:jammy, true)	2m 30s
linux (gcc, ubuntu:focal, true)	2m 39s
linux (clang, fedora:latest, true)	1m 35s
linux (clang, quay.io/centos/centos:stream9, true)	1m 58s
linux (clang, quay.io/centos/centos:stream8, true)	1m 44s
linux (clang, debian:testing, true)	3m 23s
linux (clang, debian:latest, true)	3m 7s
linux (clang, ubuntu:rolling, true)	2m 58s
linux (clang, ubuntu:jammy, true)	2m 41s
linux (clang, ubuntu:focal, true)	2m 21s
linux (gcc, quay.io/fedora/fedora:rawhide, false)	44s
linux (clang, quay.io/fedora/fedora:rawhide, false)	56s
linux (gcc, ubuntu:devel, false)	3m 13s
linux (clang, ubuntu:devel, false)	3m 22s
	1h 4m 10s

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