Fix a few uses of DeflateStream.Read

[stephentoub]

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• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
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• I have provided test coverage for my change (where applicable)
  (68 of the 71 existing PngDecoder tests already fail when run against master, before and after this change, and I'm not sure if that's expected... presumably not? Maybe I'm just doing something wrong? I'm running them in test explorer in VS2022.)

Description

The code is assuming Stream.Read always returns the requested number of bytes unless it hits EOF, but that's not guaranteed; the Stream.Read contract only guarantees at least 1 byte will be returned until EOF even if more are requested.

Fixes #1704
dotnet/runtime#55866

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[codecov]

Codecov Report

Merging #1707 (e3e2785) into master (61b137d) will increase coverage by 0.00%.
The diff coverage is 75.00%.

@@           Coverage Diff           @@
##           master    #1707   +/-   ##
=======================================
  Coverage   84.33%   84.33%           
=======================================
  Files         816      816           
  Lines       35914    35921    +7     
  Branches     4179     4183    +4     
=======================================
+ Hits        30288    30295    +7     
  Misses       4806     4806           
  Partials      820      820           

Flag	Coverage Δ
unittests	84.33% <75.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
src/ImageSharp/Formats/Png/PngDecoderCore.cs	90.65% <60.00%> (+0.03%)	⬆️
...ompression/Decompressors/DeflateTiffCompression.cs	95.65% <100.00%> (+1.20%)	⬆️

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[JimBobSquarePants]

Ah fantastic! Thanks @stephentoub

I'm not sure why you were getting test failures locally, (We have a few quirks in our setup (git submodules, LFS), were any specific errors being reported?

CI seems to be working well anyway, as does the test run on my machine.

[stephentoub]

We have a few quirks in our setup (git submodules, LFS

Ah, I bet it's LFS. I'll try to fix it tomorrow. Thanks.