[Bug]: Broken avatar placeholders for federated users in new search

[blizzz]

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

In the search dialog there is no handling for not found avatars, resulting in broken images being displayed for example for federated users.

Steps to reproduce

1. have a trusted server pairing
2. open the search dialog and there open the people one
3. check for federated users

Expected behavior

a placeholder will be shown (as long as we do not build in support for actual federated avatars)

Installation method

None

Nextcloud Server version

28

Operating system

None

PHP engine version

None

Web server

None

Database engine version

None

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

No response

List of activated Apps

No response

Nextcloud Signing status

No response

Nextcloud Logs

No response

Additional info

No response

[blizzz]

It is similar to #44287

[Fenn-CS]

#44972