[BUGFIX] Harden TcaMigration

Broken TCA - if 'config' is not an array - can lead to warnings
in TcaMigration. Move a couple of lines around to suppress this.

Change-Id: I8411cd8335de6af49cbd85f821239723dc6d6c55
Resolves: #79806
Releases: master
Reviewed-on: https://review.typo3.org/51668


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Philipp Gampe <philipp.gampe@typo3.org>
Reviewed-by: Jigal van Hemert <jigal.van.hemert@typo3.org>
Tested-by: Jigal van Hemert <jigal.van.hemert@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>