graphics/openjph: update to 0.18

This version addresses an issue, which causes illegal instruction
fault on machines that do not support AVX or more recent instruction
sets, when the code in compiled with clang and in the Release mode only.

Noticeable for anyone running Nextcloud on a machine which do not
support AVX or more recent instructions sets!

Changes: https://github.com/aous72/OpenJPH/releases/tag/0.18.0