package/libpng: bump version to 1.6.50

Release notes:
https://raw.githubusercontent.com/pnggroup/libpng/v1.6.50/ANNOUNCE

Switched _SITE to https.

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Julien Olivain <ju.o@free.fr>

package/libpng/libpng.hash

@@ -1,5 +1,5 @@
-# From https://sourceforge.net/projects/libpng/files/libpng16/1.6.49/
-sha1  ba0b3067213c53ee0e36e98824450a4f264d815d  libpng-1.6.49.tar.xz
+# From https://sourceforge.net/projects/libpng/files/libpng16/1.6.50/
+sha1  ecd92ba84628a8ace430706c85fd2fb26ba0882c  libpng-1.6.50.tar.xz
 # Locally computed:
-sha256  43182aa48e39d64b1ab4ec6b71ab3e910b67eed3a0fff3777cf8cf40d6ef7024  libpng-1.6.49.tar.xz
+sha256  4df396518620a7aa3651443e87d1b2862e4e88cad135a8b93423e01706232307  libpng-1.6.50.tar.xz
 sha256  16d9daaafbf63a31a5bdc91d4600972548fef5aaa1244202393288dbd079c49a  LICENSE

package/libpng/libpng.mk

@@ -4,10 +4,10 @@
 #
 ################################################################################
 
-LIBPNG_VERSION = 1.6.49
+LIBPNG_VERSION = 1.6.50
 LIBPNG_SERIES = 16
 LIBPNG_SOURCE = libpng-$(LIBPNG_VERSION).tar.xz
-LIBPNG_SITE = http://downloads.sourceforge.net/project/libpng/libpng$(LIBPNG_SERIES)/$(LIBPNG_VERSION)
+LIBPNG_SITE = https://downloads.sourceforge.net/project/libpng/libpng$(LIBPNG_SERIES)/$(LIBPNG_VERSION)
 LIBPNG_LICENSE = Libpng-2.0
 LIBPNG_LICENSE_FILES = LICENSE
 LIBPNG_CPE_ID_VENDOR = libpng