fixes the default markers for maps which got broken in !588

What does this MR do?

see title

How confident are you it won't break things if deployed?

quite. All icons have appeared again and no harm to be expected.

Links to related issues

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))