libpng: Update to version 1.6.45

libpng: Update to version 1.6.45

- Update from version 1.6.44 to 1.6.45
- Update of rootfile
- Changelog
    1.6.45
	  Added support for the cICP chunk.
	    (Contributed by Lucas Chollet and John Bowler)
	  Adjusted and improved various checks in colorspace calculations.
	    (Contributed by John Bowler)
	  Rearranged the write order of colorspace chunks for better conformance
	    with the PNG v3 draft specification.
	    (Contributed by John Bowler)
	  Raised the minimum required CMake version from 3.6 to 3.14.
	  Forked off a development branch for libpng version 1.8.

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>