Accepting multiple applications for same member causes assertion failure

[mnaamani]

Problem

The same member can apply more than once to an opening in the curator working group.
An assertion failure is occurring when the lead accepts more than one application for the same member because of a failed attempt to register the same role more than once on the member.

https://github.com/Joystream/substrate-runtime-joystream/blob/c63a02d922c46d11387b5e26df5dab00ec8d864a/src/content_working_group/lib.rs#L1594

This edge case was not accounted for.

Solutions

1. Prevent same member from applying more than once - if applican't wishes to perhaps increase their stake during the application process they must withdraw their application first then re-apply.

2. In fill_curator_opening() guard against successful_curator_application_ids set having applications from same member id.

3. Ensure there is always only one application per member per opening: When same member applies a second time to an opening, the new application replaces the old one.

I like Option 3 but this will require some changes in the UI/Hiring-Flow in pioneer. So I think I will prepare a fix with option 1.

[mnaamani]

This fix technically is no longer required following this #168 but we might want to keep it as a policy?

[mnaamani]

Fixed in newer versions of content directory