SDL_image: update vendored libpng from 1.6.41 to 1.6.43.

From ec8d87ed7220be3b5da81272123eaaa1d75ef783 Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Mon, 11 Mar 2024 00:37:40 +0300
Subject: [PATCH] update vendored libpng from 1.6.41 to 1.6.43.

---
 external/libpng | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/external/libpng b/external/libpng
index b3096fb3..1fcb3831 160000
--- a/external/libpng
+++ b/external/libpng
@@ -1 +1 @@
-Subproject commit b3096fb31f15538eeca4f2456f6c0e2b902cc07b
+Subproject commit 1fcb383151fc6329ad3f82cb64fc99d2b3a0b415