[BUGFIX] Fix warning in adapter service

The merge of #45415 introduced a warning
because the new meta column name was
used as array key.

Skip this step when the meta column
is found to fix this issue.

Fixes: #45415
Releases: 6.1, 6.0

Change-Id: I5446104359816d0ccacf6c239b86b9b073783174
Reviewed-on: https://review.typo3.org/18700
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel