Disposing data chunk instead of explicit returning it to ArrayPool in PngDecoderCore.Identify

[denisivan0v]

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

The new Image.Identify API was introduced in #292. In #475 memory management was significantly improved, but there is still a case for png format when ArrayPool is used directly when calling Image.Identify, not with IManagedByteBuffer API.
This leads to the issue when ArgumentException is throwing in ArrayPool.Return method with this message:

The buffer is not associated with this pool and may not be returned to it.
Parameter name: array

This PR fixes this problem.

[JimBobSquarePants]

Hi @denisivan0v

Good catch! I'll get this merged once the CI finished 👍

[codecov]

Codecov Report

Merging #534 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #534      +/-   ##
=========================================
- Coverage   87.21%   87.2%   -0.02%     
=========================================
  Files         842     842              
  Lines       35452   35451       -1     
  Branches     2627    2627              
=========================================
- Hits        30920   30914       -6     
- Misses       3763    3767       +4     
- Partials      769     770       +1

Impacted Files	Coverage Δ
src/ImageSharp/Formats/Png/PngDecoderCore.cs	68.37% <100%> (-0.07%)	⬇️
tests/ImageSharp.Tests/TestFileSystem.cs	63.63% <0%> (-13.64%)	⬇️
tests/ImageSharp.Tests/TestFormat.cs	75% <0%> (-2.39%)	⬇️

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[denisivan0v]

Many thanks @JimBobSquarePants! 🎉

[JimBobSquarePants]

No worries! Thanks for the PR! 😄