[BUGFIX] Fixed bug if DCE has no field values

$this->settings in DceController may be empty, eg. if a DCE
contains just one sectionfield, which has no values.

In this case $this->settings is NULL and throws an exception
if the typoScriptUtility tries to render the configuration array.

Now in such cases an empty array will be passed, instead of
NULL.

Resolves: #60985

Change-Id: I21d0675edc5dc36f73298c606b2f15deb89d513f
Reviewed-on: http://review.typo3.org/32172
Reviewed-by: Armin Ruediger Vieweg <armin@v.ieweg.de>
Tested-by: Armin Ruediger Vieweg <armin@v.ieweg.de>