[png-mng-implement] libpng-1.6.30beta04 is available

[Glenn Randers-Pehrson]

libpng-1.6.30beta04 is available from
https://ftp-osl.osuosl.org/pub/libpng/src/beta/libpng16
ftp://ftp-osl.osuosl.org/pub/libpng/src/beta/libpng16
and from
http://libpng.sf.net


Version 1.6.30beta04 [June 7, 2017]
Avoid writing an empty IDAT when the last IDAT exactly fills the
compression buffer (bug report by Brian Baird). This bug was
introduced in libpng-1.6.0.

Glenn