[BUGFIX] RTE: Incorrect height of the RTE framework

The calculated height of the toolbar is incorrect due to floating
elements.

Releases: master
Resolves: #63964
Change-Id: I771a0f3f31112777d6d2b8507c23d93f359c24b3
Reviewed-on: http://review.typo3.org/35554
Reviewed-by: Stanislas Rolland <typo3@sjbr.ca>
Tested-by: Stanislas Rolland <typo3@sjbr.ca>