RFR: JDK-8316030: Update Libpng to 1.6.40

[Damon Nguyen]

On Tue, 17 Oct 2023 17:27:45 GMT, Harshitha Onkar <honkar at openjdk.org> wrote:

> Libpng updated from 1.6.39 to 1.6.40
> 
> Build and CI Testing passes on all platforms.

Changes look good to me. I left one question for clarification for myself.

src/java.desktop/share/native/libsplashscreen/libpng/pngget.c line 60:

> 58:       if (flag == PNG_INFO_tRNS && png_ptr->num_trans == 0)
> 59:          return(0);
> 60: #endif

What's this addition doing exactly?

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Marked as reviewed by dnguyen (Committer).

PR Review: https://git.openjdk.org/jdk/pull/16223#pullrequestreview-1688152478
PR Review Comment: https://git.openjdk.org/jdk/pull/16223#discussion_r1365803799