return stoptimesForDate from the schedule if it is called with no parameter on a day when the trip does not run

[tkalvas]

Fixes Issue #6475

Technically the solution here is wrong, but longstanding UIs (like digitransit-ui) rely on getting the scheduled timetable when running stoptimesForDate without a parameter on a wrong day.

[codecov]

Codecov Report

Attention: Patch coverage is 57.14286% with 6 lines in your changes missing coverage. Please review.

Project coverage is 70.18%. Comparing base (04fadbf) to head (6a28d6a).
Report is 24 commits behind head on dev-2.x.

Files with missing lines	Patch %	Lines
...ipplanner/apis/gtfs/datafetchers/StoptimeImpl.java	33.33%	2 Missing ⚠️
...entripplanner/apis/gtfs/datafetchers/TripImpl.java	50.00%	1 Missing and 1 partial ⚠️
...planner/transit/service/DefaultTransitService.java	71.42%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-2.x    #6480      +/-   ##
=============================================
- Coverage      70.20%   70.18%   -0.02%     
+ Complexity     18313    18312       -1     
=============================================
  Files           2080     2082       +2     
  Lines          77182    77194      +12     
  Branches        7831     7830       -1     
=============================================
- Hits           54183    54177       -6     
- Misses         20230    20250      +20     
+ Partials        2769     2767       -2     

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