pol.is reports won't generate under rare circumstances

[alexrandaccio]

Describe the bug
When a Conversation Stage ends, a link to a pol.is report is generated automatically. However, if pol.is has not created the report yet, the link will not be generated. Since this function is only called once, this means the report will not be visible.

To Reproduce
Steps to reproduce the behavior:

1. Create a new event with a short delegation stage and a short conversation stage
2. during the conversation stage, open the conversation and participate. this will generate the pol.is conversation
3. if the conversation stage ends quickly enough, pol.is will not have had time to generate a report. open the conversation again and you will see that no report appears. no matter how long you wait the report will not appear, because the Voice app only requests the pol.is api once.

Expected behavior
whenever pol.is has created the report, it should appear on the Voice app

Proposed Solution
after a conversation has ended, we should call generate_report() every time a user accesses the conversation page, until it succeeds.