A couple of small tweaks of the getPdfFilenameFromUrl helper

[Snuffleupagus]

• Shorten the getURL function slightly, by re-factoring the try-catch blocks.
• Change how the decode function looks for a decoded ".pdf" name, to skip the regular expression matching when it's not needed and to allow re-using the already defined pdfRegex.

Smaller diff with https://github.com/mozilla/pdf.js/pull/21222/changes?w=1

[codecov-commenter]

Codecov Report

❌ Patch coverage is 62.50000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.96%. Comparing base (a55cec4) to head (8fc5677).

Files with missing lines	Patch %	Lines
src/display/display_utils.js	62.50%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21222      +/-   ##
==========================================
- Coverage   55.97%   55.96%   -0.01%     
==========================================
  Files         218      218              
  Lines       59033    59033              
==========================================
- Hits        33041    33037       -4     
- Misses      25992    25996       +4     

Flag	Coverage Δ
fonttest	8.67% <ø> (ø)
unittest	55.20% <62.50%> (-0.03%)	⬇️
unittestcli	55.72% <62.50%> (ø)

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[timvandermeij]

r=me; thank you for flattening this code a bit!