[BUGFIX] load TCA before manipulation

Load the TCA before manipulating the contents in form and
css_styled_content, otherwise the checks for later calls to
loadTCA will fail while the TCA is not fully loaded.

Change-Id: Id2d96d8dab0fc53661689f778871ebb078272062
Resolves: #38505
Releases: 6.1, 6.0, 4.7, 4.6, 4.5
Reviewed-on: https://review.typo3.org/17943
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn