Intervention (speech type): switch to other types results on error message

[MSoeb]

Description: If a user selects intervention as a speech type in the list of speakers, a switch to for example contribution results in an error message. To change the speech type, the user needs to deselect the intervention and then select forspeech.

Error message:

Reproduction:

1. open a meeting
2. activate in settings > list of speakers > forspeech, star icon and intervention by adding time value
3. go to agenda and create an item. add a person to the list of speakers. Select intervention and switch it to forspeech.

What should happen:
The switch between different speech types should not result in an errror message. It should easily be possible to perform a switch. (Affected speech types are Forspeech, Contra Speech and Contribution)