jurt: Use <T> T[] toArray(T[] a)

http://docs.oracle.com/javase/1.5.0/docs/api/java/util/Set.html#toArray%28T%5b%5d%29

Change-Id: I601e77db3cc978d81aebddfe6abba1c020671913
Reviewed-on: https://gerrit.libreoffice.org/10853
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>