libpng warning: bKGD: invalid

[jwrober]

Describe the bug If you start the client from command-line, you see three of the messages in the title.

To Reproduce Steps to reproduce the behavior:

1. Start client from command-line
2. See error

Expected behavior Don't see the error Would be good for the message to tell what image is throwing the error so we can fix it

Screenshots N/A

Platform and version (please complete the following information):

• OS: Linux
• Freeciv21 version: 3.1-beta.1
• Ruleset/Longturn game (if applicable): N/A

Additional context Found while testing PR 2288, but don't think its related.

[lmoureaux]

Cannot repro. Could it be from a modpack? Which libpng version do you have?

[lmoureaux]

I'm also getting it now. Context:

[critical] freeciv21-client (/home/louis/Personal/freeciv21/client/tileset/tilespec.cpp:1240) - Could not load gfx file "flags/congofreestate-shield".
[warning] freeciv21-client (unknown:0) - libpng warning: bKGD: invalid