[BUG] Closing a roll call fails in some execution flows

[matteosz]

Description (Actual behavior)

These errors are generated from the servers.

It happens when the organizer creates and opens a Roll Call X, creates a Roll Call Y and finally tries to close X. The error message is the following: An error response was replied by the server

Error -4 - invalid message field: failed to publish: failed to handle publish message: failed to process message: failed to process action 'roll_call#close': The roll call cannot be closed since it's not open] com.github.dedis.popstellar.utility.error.JsonRPCErrorException: Error -4 - invalid message field: failed to publish: failed to handle publish message: failed to process message: failed to process action 'roll_call#close': The roll call cannot be closed since it's not open

Expected behavior

The errors shouldn't happen.

Version & Environment

This bug was reproduced on this commit, however it was present since this other commit.

Front-ends:

• [ ] Fe1-Web (please include browser's names & version)
• [ ] Fe2-Android (please specify if phone or emulation, and Android version)
• [X] Not applicable

Back-ends:

• [X] Be1-Go
• [X] Be2-Scala
• [ ] Not applicable

Impact

The user cannot close the roll call, and thus open any new one (as two roll calls cannot be opened at the same time)