Fixed OOM issue when reading partially corrupted PDFs

[akopachov]

I encountered multiple PDFs that appeared to be partially corrupted. As a result, PDF.js was unable to load them due to an out‑of‑memory (OOM) error.

This PR fixes the issue, and I can confirm that with this change in place I am now able to successfully load those PDFs.

Unfortunately, I can’t include or share the affected PDFs due to NDA restrictions. However, I suspect they may have been generated using one of the online “PDF combine” services. In terms of content, the PDFs each contain around 10–15 pages with a mix of scanned images and text.

[calixteman]

Sorry but I'm not super excited with having such a patch without a test and a pdf.
You can send me a pdf on my pro email (you can find it here: https://bugzilla.mozilla.org/enter_bug.cgi?product=Firefox&component=PDF%20Viewer, I'm the triage owner of the pdf component). If you can't because the pdf is too much confidential, that's fine but you need edit it yourself in order to remove whatever has to be private.
If you understand well enough the underlying problem, you can create a very basic one in using a text editor which render correctly in Acrobat or Chrome but not with pdf.js.

[akopachov]

Will try to prepare some test PDF.
Thank you.

[Snuffleupagus]

Any "magical" values/constants should always have a good comment explaining why they are needed and how they were chosen.

[akopachov]

Makes sense. Thank you.
I added the comment explaining where and why I picked this magic value from, but I'm open to any discussion if it should be set to some more reasonable value.

[Snuffleupagus]

Given that PDF.js is first and foremost intended for browsers, using Node.js to choose that value seems a little strange.

---

Also, please see https://github.com/mozilla/pdf.js/wiki/Squashing-Commits

[codecov-commenter]

Codecov Report

❌ Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 62.78%. Comparing base (909a700) to head (f08d965).
⚠️ Report is 352 commits behind head on master.

Files with missing lines	Patch %	Lines
src/core/xref.js	93.33%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #20723   +/-   ##
=======================================
  Coverage   62.77%   62.78%           
=======================================
  Files         169      169           
  Lines      119824   119832    +8     
=======================================
+ Hits        75224    75234   +10     
+ Misses      44600    44598    -2     

Flag	Coverage Δ
fonttest	7.64% <ø> (ø)
unittestcli	62.75% <93.33%> (+<0.01%)	⬆️

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