Bug when publishing rankings based on a custom attribute

[joergewald]

1. Imported an FSDB file which defines a custom attribute "SportClass" for every pilot
2. Added a ranking "Sports Class", based on custom attribute "SportClass"=1
3. Checking tracks and scoring worked fine.
4. Published the results.
5. Calling up the results HTML gave this error:

[2021-05-29 13:06:07,923] ERROR in app: Exception on /task_result/9 [GET]
Traceback (most recent call last):
File "/home/sid/.local/lib/python3.8/site-packages/flask/app.py", line 2447, in wsgi_app
response = self.full_dispatch_request()
File "/home/sid/.local/lib/python3.8/site-packages/flask/app.py", line 1952, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/home/sid/.local/lib/python3.8/site-packages/flask/app.py", line 1821, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/home/sid/.local/lib/python3.8/site-packages/flask/_compat.py", line 39, in reraise
raise value
File "/home/sid/.local/lib/python3.8/site-packages/flask/app.py", line 1950, in full_dispatch_request
rv = self.dispatch_request()
File "/home/sid/.local/lib/python3.8/site-packages/flask/app.py", line 1936, in dispatch_request
return self.view_functionsrule.endpoint
File "/app/airscore/public/views.py", line 510, in task_result
result_file = frontendUtils.get_pretty_data(file)
File "/app/airscore/core/frontendUtils.py", line 1452, in get_pretty_data
and r['custom'][str(s['attr_id'])] == s['rank_value'])
KeyError: '3'

6. Removed the "Sports Class" ranking
7. Re-scored, re-published the results
8. Now calling up the results HTML worked fine

It would seem that producing the results HTML for rankings based on custom attributes is broken.