[BUGFIX] Do not add already existing columns to TCA

Resolves: #62958
Change-Id: I9734b56b6287012cde508df06ddbdd25e2d86b01
Reviewed-on: http://review.typo3.org/34297
Reviewed-by: Tim Lochmüller <tim@fruit-lab.de>
Tested-by: Tim Lochmüller <tim@fruit-lab.de>