BMFF Performance boost: don't read boxes we're not interested in (backport #1974)

[mergify]

This is an automatic backport of pull request #1974 done by Mergify.
Cherry-pick of 4e587fa has failed:

On branch mergify/bp/0.27-maintenance/pr-1974
Your branch is up to date with 'origin/0.27-maintenance'.

You are currently cherry-picking commit 4e587fa9.
  (fix conflicts and run "git cherry-pick --continue")
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  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   src/bmffimage.cpp

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[codecov]

Codecov Report

Merging #1975 (69f976b) into 0.27-maintenance (1f950b0) will increase coverage by 0.01%.
The diff coverage is 75.00%.

❗ Current head 69f976b differs from pull request most recent head 07d3f7a. Consider uploading reports for the commit 07d3f7a to get more accurate results

@@                 Coverage Diff                  @@
##           0.27-maintenance    #1975      +/-   ##
====================================================
+ Coverage             46.32%   46.33%   +0.01%     
====================================================
  Files                   146      146              
  Lines                 22950    22957       +7     
  Branches              11781    11784       +3     
====================================================
+ Hits                  10632    10638       +6     
  Misses                 6702     6702              
- Partials               5616     5617       +1     

Impacted Files	Coverage Δ
src/bmffimage.cpp	41.84% <75.00%> (+0.82%)	⬆️

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