Fix ExposeSwaggerDocumentUrlsRoute behaviour

[martincostello]

Fix SwaggerUIOptions.ExposeSwaggerDocumentUrlsRoute not being respected.

Fixes #3983.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.04%. Comparing base (c3071ad) to head (1190461).
⚠️ Report is 5 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4000   +/-   ##
=======================================
  Coverage   95.04%   95.04%           
=======================================
  Files         111      111           
  Lines        3958     3959    +1     
  Branches      801      802    +1     
=======================================
+ Hits         3762     3763    +1     
  Misses        196      196           

Flag	Coverage Δ
Linux	95.04% <100.00%> (+<0.01%)	⬆️
Windows	95.04% <100.00%> (+<0.01%)	⬆️
macOS	95.04% <100.00%> (+<0.01%)	⬆️

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