[BUGFIX] root-lines for DB Mounts in Pagetree rendering wrong markup

The option "options.pageTree.showPathAboveMounts = 1" which shows the
rootline of each DB Mount in a line before is implemented in a
non-valid way.

This means, that a <div> tag is rendered within an <ul> tag right in
front of the <li> of the DB Mount node.

Change-Id: Ic715426b8d04220410bcb15bfba33a39e5fd47bc
Fixes: #31067
Releases: 4.6
Reviewed-on: http://review.typo3.org/5962
Reviewed-by: Xavier Perseguers
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Francois Suter
Tested-by: Francois Suter