STANBOL-975: Fixes this by (1) catching NoSuchElementException for SortedSet#last() and (2) optaining a local reference to the ServiceTracker for the labelTokenizer and checking it for NOT beeing NULL

git-svn-id: https://svn.apache.org/repos/asf/stanbol/trunk@1453716 13f79535-47bb-0310-9956-ffa450edef68