FPII-2034: DO NOT MERGE Update libpng to 1.6.20

DO NOT MERGE Update libpng to 1.6.20

BUG:23265085
Change-Id: I2fc2106965c789a54f04412e9c63a0901b0c1e71
(cherry picked from commit 0b39f202aaedd3029e4270d2af7d58ba6634f9cd)
diff --git a/tests/pngimage-full b/tests/pngimage-full
index f5eb989..1198ed0 100755
--- a/tests/pngimage-full
+++ b/tests/pngimage-full
@@ -1,2 +1,2 @@
 #!/bin/sh
-exec ./pngimage --exhaustive --log "${srcdir}/contrib/pngsuite/"*.png
+exec ./pngimage --exhaustive --list-combos --log "${srcdir}/contrib/pngsuite/"*.png