Fix padding removal for 3d input in MSSSIM

[SkafteNicki]

What does this PR do?

Fixes #1656

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• Did you make sure to update the docs?
• Did you write any new necessary tests?

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[codecov]

Codecov Report

Merging #1674 (f3f0b0c) into master (9d3a7cc) will decrease coverage by 47%.
The diff coverage is 100%.

❗ Current head f3f0b0c differs from pull request most recent head 099567c. Consider uploading reports for the commit 099567c to get more accurate results

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #1674     +/-   ##
========================================
- Coverage      89%     42%    -47%     
========================================
  Files         228     228             
  Lines       12796   12798      +2     
========================================
- Hits        11363    5365   -5998     
- Misses       1433    7433   +6000