[BUGFIX] Code completion in t3editor behind operator

Fix code completion in t3editor when substituing a value with
completed code behind a typoscript operator.

Change-Id: Id1fbb99aba850ee0787dba4b8562d0a22c119979
Resolves: #25594
Releases: master, 6.2
Reviewed-on: http://review.typo3.org/36804


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Benjamin Mack <benni@typo3.org>