[+BUGFIX] Fluid (ViewHelpers): RenderViewHelper works with TYPO3

In I14c6dd4d9db13a98f1873a79bb43fbf299d2c835, we have introduced
a change which caused the Menu generation in TYPO3 Phoenix to crash,
as {settings} is not available in these templates.

Now, a check has been added which checks for {settings} being present.

Additionally, a unit test has been written testing this behavior.