Log Message:
png: update to 1.6.44.

Changes from version 1.6.43 to version 1.6.44
---------------------------------------------

 * Hardened calculations in chroma handling to prevent overflows, and
   relaxed a constraint in cHRM validation to accomodate the standard
   ACES AP1 set of color primaries.
   (Contributed by John Bowler)
 * Removed the ASM implementation of ARM Neon optimizations and updated
   the build accordingly. Only the remaining C implementation shall be
   used from now on, thus ensuring the support of the PAC/BTI security
   features on ARM64.
   (Contributed by Ross Burton and John Bowler)
 * Fixed the pickup of the PNG_HARDWARE_OPTIMIZATIONS option in the
   CMake build on FreeBSD/amd64. This is an important performance fix
   on this platform.
 * Applied various fixes and improvements to the CMake build.
   (Contributed by Eric Riff, Benjamin Buch and Erik Scholz)
 * Added fuzzing targets for the simplified read API.
   (Contributed by Mikhail Khachayants)
 * Fixed a build error involving pngtest.c under a custom config.
   This was a regression introduced in a code cleanup in libpng-1.6.43.
   (Contributed by Ben Wagner)
 * Fixed and improved the config files for AppVeyor CI and Travis CI.