Update bundled libpng to version 1.6.42

[ChangeLog][Third-Party Code] libpng was updated to version 1.6.42

Pick-to: 6.7 6.6 6.6.2 6.5 6.2 5.15
Change-Id: Ie41c2df610fcd456af2bc4dee05dde90c426602b
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

src/3rdparty/libpng/ANNOUNCE

@@ -1,4 +1,4 @@
-libpng 1.6.41 - January 24, 2024
+libpng 1.6.42 - January 29, 2024
 ================================
 
 This is a public release of libpng, intended for use in production code.
@@ -9,13 +9,13 @@ Files available for download
 
 Source files with LF line endings (for Unix/Linux):
 
- * libpng-1.6.41.tar.xz (LZMA-compressed, recommended)
- * libpng-1.6.41.tar.gz (deflate-compressed)
+ * libpng-1.6.42.tar.xz (LZMA-compressed, recommended)
+ * libpng-1.6.42.tar.gz (deflate-compressed)
 
 Source files with CRLF line endings (for Windows):
 
- * lpng1641.7z (LZMA-compressed, recommended)
- * lpng1641.zip (deflate-compressed)
+ * lpng1642.7z (LZMA-compressed, recommended)
+ * lpng1642.zip (deflate-compressed)
 
 Other information:
 
@@ -25,6 +25,14 @@ Other information:
  * TRADEMARK.md
 
 
+Changes from version 1.6.41 to version 1.6.42
+---------------------------------------------
+
+ * Fixed the implementation of the macro function `png_check_sig`.
+   This was an API regression, introduced in libpng-1.6.41.
+   (Reported by Matthieu Darbois)
+
+
 Changes from version 1.6.40 to version 1.6.41
 ---------------------------------------------
 

src/3rdparty/libpng/CHANGES

@@ -6134,7 +6134,7 @@ Version 1.6.41 [January 24, 2024]
     (Contributed by GuXiWei, JinBo and ZhangLixia)
   Fixed the run-time discovery of MIPS MSA hardware.
     (Contributed by Sui Jingfeng)
-  Fixed an off-by-one error in the function `png_do_check_palette_indexes`,
+  Fixed an off-by-one error in the function png_do_check_palette_indexes(),
     which failed to recognize errors that might have existed in the first
     column of a broken palette-encoded image. This was a benign regression
     accidentally introduced in libpng-1.6.33. No pixel was harmed.
@@ -6161,6 +6161,11 @@ Version 1.6.41 [January 24, 2024]
   Improved the test coverage.
     (Contributed by John Bowler)
 
+Version 1.6.42 [January 29, 2024]
+  Fixed the implementation of the macro function png_check_sig().
+    This was an API regression, introduced in libpng-1.6.41.
+    (Reported by Matthieu Darbois)
+
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src/3rdparty/libpng/README

@@ -1,4 +1,4 @@
-README for libpng version 1.6.41
+README for libpng version 1.6.42
 ================================
 
 See the note about version numbers near the top of `png.h`.