[BUGFIX] Fix parsing of IF structures

Fix a regression introduced during the latest change to the
parsing of IF structures.

Resolves: #63358
Releases: 1.8
Change-Id: Ia54a66b53000eba6d353c1a9b76a397ceb31003f
Reviewed-on: http://review.typo3.org/34673
Reviewed-by: Francois Suter <francois@typo3.org>
Tested-by: Francois Suter <francois@typo3.org>