[BUGFIX] Fluid templates need extra whitespace to avoid render error

If a fluid template is empty or just contain namespace declarations without
trailing whitespaces an error appears while fluid renders the template.

To avoid this bug the templates get a trailing space before rendering.
After rendering the a trim will be performed on result.

Resolves: #60024
Change-Id: Id982dad0d4bbdfded8890ee9d42f097840f6df8c
Reviewed-on: https://review.typo3.org/31261
Reviewed-by: Armin Ruediger Vieweg
Tested-by: Armin Ruediger Vieweg