[ticket/11548] Fix incorrect usage of array_map on acp groups page

The array_map was only ran on small parts of the actual error array instead
of the whole one. This resulted in the output of the language variables' names
rather than their actual value.

PHPBB3-11548
Merge remote-tracking branch 'marc1706/ticket/11548-develop-olympus' into develop-olympus

* marc1706/ticket/11548-develop-olympus:
  [ticket/11548] Fix incorrect usage of array_map on acp groups page