Png decoder fix for Issue #1014

[brianpopow]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following matches the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules 👮.
• I have provided test coverage for my change (where applicable)

Description

This PR fixes an issue when decoding PNG where data would spread over multiple IDAT chunks.

[JimBobSquarePants]

Oh wow! Amazing! I was so worried about those issues.

Thanks so much for helping out here, it’s really really appreciated!

[codecov]

Codecov Report

Merging #1020 into master will decrease coverage by <.01%.
The diff coverage is 91.3%.

@@            Coverage Diff             @@
##           master    #1020      +/-   ##
==========================================
- Coverage   89.87%   89.87%   -0.01%     
==========================================
  Files        1103     1103              
  Lines       48877    48897      +20     
  Branches     3441     3441              
==========================================
+ Hits        43929    43945      +16     
- Misses       4246     4249       +3     
- Partials      702      703       +1

Impacted Files	Coverage Δ
tests/ImageSharp.Tests/TestImages.cs	100% <ø> (ø)	⬆️
...ts/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs	100% <100%> (ø)	⬆️
...c/ImageSharp/Formats/Png/Zlib/ZlibInflateStream.cs	57.33% <83.33%> (-3.78%)	⬇️
...eSharp.Tests/Formats/Png/PngDecoderTests.Chunks.cs	100% <0%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f4fecd5...fdab536. Read the comment docs.

[brianpopow]

@JimBobSquarePants maybe at the end of the Issue1014 unit test a image.CompareToOriginal(provider, ImageComparer.Exact); could be added, just to make sure.

[antonfirsov]

Yeah definitely, let's always include validating tests in all PR-s!

[JimBobSquarePants]

Yes, missed that it wasn’t there in my excitement!