Meeting edit view: search field didn't load

[MSoeb]

Description: If a superadmin or organization-admin wants to add an account as a new admin via the meeting dialog, the search field didn't load, if the meeting has other accounts as meeting admins. Only the account list is visible without the search field.

Reproduction:

1. open committee as superadmin: create a new com. and create a new meeting. Save it.
2. open the meeting edit view again and try to add another user. Search field is missing
3. Hint: Eventually another extra user is required to trigger this. If pos. 2. fails, please add a another user.

What should happen:
The search field should always appear in the meeting edit view.

[emanuelschuetze]

same like #2925