Improve error handling in the PDFFindController.prototype.#extractText method

[Snuffleupagus]

• Improve error handling in the PDFFindController.prototype.#extractText method

  This handles all errors correctly, if e.g. the document is closed in the middle of searching.
  Also, replacing the "promise chains" with more await helps simplify the code a little bit.

• Avoid setting page-content for a previous document in the PDFFindController.prototype.#extractText method

  Given that all of the relevant API methods are asynchronous it's possible, although quite unlikely, that the existing "is the document active" check won't catch all situations where the document was closed in the middle of searching.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 61.11111% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.89%. Comparing base (34c3ee1) to head (aa08b02).

Files with missing lines	Patch %	Lines
web/pdf_find_controller.js	61.11%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21197      +/-   ##
==========================================
- Coverage   55.94%   55.89%   -0.06%     
==========================================
  Files         218      218              
  Lines       59062    59066       +4     
==========================================
- Hits        33043    33014      -29     
- Misses      26019    26052      +33     

Flag	Coverage Δ
fonttest	?
unittest	55.05% <61.11%> (+<0.01%)	⬆️
unittestcli	55.71% <61.11%> (+0.01%)	⬆️

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[calixteman]

LGTM. Thank you.

[timvandermeij]

Thank you for helping out with this!