Rounds missing from my-studies API endpoint for contributors

[fitztrev]

Steps to reproduce

2 user accounts used: bobby (the owner) and mary (a contributor)

1. As bobby

   1. Create a broadcast with 2 rounds:

      http -A bearer -a lip_bobby POST http://localhost:8080/broadcast/new name=Testing

      TOUR_ID=keWiXSoM
      http -A bearer -a lip_bobby POST http://localhost:8080/broadcast/$TOUR_ID/new name=round1
      http -A bearer -a lip_bobby POST http://localhost:8080/broadcast/$TOUR_ID/new name=round2

   2. In the UI, add mary as a member/contributor

2. As mary
   1. Get your rounds

      http -A bearer -a lip_mary http://localhost:8080/api/broadcast/my-rounds

      One of the 2 rounds is missing

In the mongodb study collection, mary is added a member but is missing from the uids of the other document. Manually adding mary to uids causes the round to be included in the my-rounds response.