libpng: security bump to version 1.6.16

Fixes a buffer overflow which may allow an attacker to gain write
access to memory.
CVE requested but not yet assigned.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/libpng/libpng.hash

@@ -1,3 +1,3 @@
-# From http://sourceforge.net/projects/libpng/files/libpng16/1.6.15/
-md5	a95cb387c53215b034203b41ec57c7e5	libpng-1.6.15.tar.xz
-sha1	bddeac8ca97fbcf54d6d32c6eefed5d94b49df88	libpng-1.6.15.tar.xz
+# From http://sourceforge.net/projects/libpng/files/libpng16/1.6.16/
+md5	23b7286b5d4a86de950fd2ffc5cac742	libpng-1.6.16.tar.xz
+sha1	31855a8438ae795d249574b0da15b34eb0922e13	libpng-1.6.16.tar.xz

package/libpng/libpng.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-LIBPNG_VERSION = 1.6.15
+LIBPNG_VERSION = 1.6.16
 LIBPNG_SERIES = 16
 LIBPNG_SOURCE = libpng-$(LIBPNG_VERSION).tar.xz
 LIBPNG_SITE = http://downloads.sourceforge.net/project/libpng/libpng${LIBPNG_SERIES}/$(LIBPNG_VERSION)