libpng: upgrade to release 1.6.37

Fixes CVE-2019-7317.

Change-Id: I3374f5cbd6552e2c1569d63ee680d0c1d9389621
Reviewed-on: https://gerrit.libreoffice.org/71663
Tested-by: Jenkins
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>
(cherry picked from commit e2abbc00)
Reviewed-on: https://gerrit.libreoffice.org/71670Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
Tested-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

download.lst

@@ -204,8 +204,8 @@ export PDFIUM_SHA256SUM := 80331b48166501a192d65476932f17044eeb5f10faa6ea50f4f17
 export PDFIUM_TARBALL := pdfium-3426.tar.bz2
 export PIXMAN_SHA256SUM := 21b6b249b51c6800dc9553b65106e1e37d0e25df942c90531d4c3997aa20a88e
 export PIXMAN_TARBALL := e80ebae4da01e77f68744319f01d52a3-pixman-0.34.0.tar.gz
-export LIBPNG_SHA256SUM := 2f1e960d92ce3b3abd03d06dfec9637dfbd22febf107a536b44f7a47c60659f6
-export LIBPNG_TARBALL := libpng-1.6.34.tar.xz
+export LIBPNG_SHA256SUM := 505e70834d35383537b6491e7ae8641f1a4bed1876dbfe361201fc80868d88ca
+export LIBPNG_TARBALL := libpng-1.6.37.tar.xz
 export POPPLER_SHA256SUM := 92e09fd3302567fd36146b36bb707db43ce436e8841219025a82ea9fb0076b2f
 export POPPLER_TARBALL := poppler-0.74.0.tar.xz
 export POSTGRESQL_SHA256SUM := db61d498105a7d5fe46185e67ac830c878cdd7dc1f82a87f06b842217924c461