Fix 2 buffer overflows in TIFF decoding

[hugovk]

No description provided.

[codecov]

Codecov Report

Merging #4507 into master will decrease coverage by 0.63%.
The diff coverage is 40%.

@@            Coverage Diff            @@
##           master   #4507      +/-   ##
=========================================
- Coverage   89.83%   89.2%   -0.64%     
=========================================
  Files         328     326       -2     
  Lines       40833   40842       +9     
=========================================
- Hits        36683   36433     -250     
- Misses       4150    4409     +259

Flag	Coverage Δ
#AppVeyor	?
#GHA_Docker	85.94% <40%> (-0.01%)	⬇️
#GHA_Ubuntu	87.91% <40%> (-0.13%)	⬇️
#GHA_Windows	?
#GHA_macOS	87.03% <40%> (-0.02%)	⬇️
#TravisCI	92.66% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
src/libImaging/TiffDecode.c	83.33% <40%> (-1.58%)	⬇️
Tests/test_imagewin_pointers.py	7.69% <0%> (-92.31%)	⬇️
Tests/test_imagewin.py	44.23% <0%> (-55.77%)	⬇️
Tests/test_locale.py	73.33% <0%> (-26.67%)	⬇️
src/PIL/ImageWin.py	35.22% <0%> (-25%)	⬇️
Tests/test_file_wmf.py	75% <0%> (-25%)	⬇️
src/PIL/WmfImagePlugin.py	74.62% <0%> (-20.9%)	⬇️
src/PIL/ImageGrab.py	75.86% <0%> (-20.69%)	⬇️
Tests/test_imagefont_bitmap.py	91.3% <0%> (-8.7%)	⬇️
src/PIL/ImageShow.py	83.33% <0%> (-7.85%)	⬇️
... and 35 more

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[hugovk]

The 8d4fdf6 commit to "Use actions/checkout@v2 to fix checkout after restarts" isn't helping for Windows:

Removing from this PR, can deal with it after the release.

[hugovk]

This is showing some older failed GHA Windows jobs, but also showing the re-runs as green. To double check, here's the same GHA jobs passing on my fork: hugovk#47.

Merging.