Fix #71316: libpng warning from imagecreatefromstring

[cmb69]

We backport the respective upstream fix[1] to our bundled libgd, and
add a regression test, too.

[1] libgd/libgd@636100b

[nikic]

Looks okay, though it would be nice to have a more targeted test image.

[cmb69]

I tried to come up with a smaller test image long ago, but failed, and that was basically the reason why I didn't fix that issue in libgd; now they fixed it without any test case.

[nikic]

Well, we could do the same then :)

[cmb69]

Okay, I applied without the test.

[mmarquez]

I've a site with PHP 8.0.14 and I've found an image that raise the same error https://imgur.com/a/XwVKwxr

[cmb69]

@mmarquez, your GD is likely built against system libgd.

[dzuelke]

@cmb69 issue is back here on 8.0.14, built against bundled libgd:

$ readelf -d .heroku/php/lib/php/extensions/no-debug-non-zts-20210902/gd.so | grep NEEDED
 0x0000000000000001 (NEEDED)             Shared library: [libz.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libpng16.so.16]
 0x0000000000000001 (NEEDED)             Shared library: [libwebp.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libjpeg.so.8]
 0x0000000000000001 (NEEDED)             Shared library: [libfreetype.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]

Downgrading to 8.0.13 fixes it; no warnings.

[dzuelke]

Okay so I guess this is from 1919c4b; is the recommended way then really to prefix all load operations with @?

[dzuelke]

And/or should there be a setting similar to gd.jpeg_ignore_warning?

The problem is that there is no gd_last_error() or similar, so it's hard to programmatically capture these warnings.

[cmb69]

@dzuelke, yes, I think there should be something like gd.jpeg_ignore_warning. And some gd_last_error() might be a good idea as well, although I'm not really sure about that.

[brettwhiteman]

I've submitted a PR to actually fix the problem in the bundled GD code
#8002