Camel-ical: Camel-20370 brought a NPE in some cases

With the recent change https://github.com/apache/camel/commit/b9ec2cbf8aef4b3b86b9bb4be9ac9cb8a5bc3241 - setter setValidating on ICalDataFormat may throw a NullPoinerException, because the underlying object - outputter is null. 

Local variable (which is present but unset) should be used.