Relaxed handle of corrupt png files

[svenclaesson]

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Description

WIP support for handing truncated png files

Implementing an option for PngDecoder, IgnoreCrcErrors Tried it a bit but got stuck by the fact that IDAT and IEND is considered critical chunks and found no way of ignoring that fact if the file is truncated, IDAT is cut off and IEND is missing.

This file is truncated and i'm trying to get a partial result converted as libpng (chrome) and WIC can do.

Maybe you have some pointers for me

See https://github.com/SixLabors/ImageSharp/issues/2570

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[JimBobSquarePants]

@svenclaesson could you please explicitly invite me to contribute to your fork. I need to add the test image from above and due to a quirk in Git LFS permissions with GitHub I cannot push any images to your fork without being invited.

@dlemstra is there a way to get the Magick decoder to break on adaptive filter errors? When I try to use your decoder as a reference for this file the following exception is thrown.

ImageMagick.MagickCoderErrorException : bad adaptive filter value `' @ error/png.c/MagickPNGErrorHandler/1716

[JimBobSquarePants]

Thanks for the invite. @svenclaesson

I've now reworked the decoder to allow granular control of CRC checking and also allow us to decode the provided image.

[svenclaesson]

Thanks for working on this