Run on unseen material without annotations

[eponvert]

When passing a test file to chunk.py, if it does not have annotations for evaluation, we currently have this error:

Exception in thread "main" java.lang.AssertionError
    at upparse.corpus.UnlabeledBracketSet.fromTokens(UnlabeledBracketSet.java:113)
    at upparse.corpus.UnlabeledBracketSet.fromString(UnlabeledBracketSet.java:97)
    at upparse.corpus.CCLParserCorpusTreeIter.getNext(CCLParserCorpusTreeIter.java:17)
    at upparse.corpus.CCLParserCorpusTreeIter.getNext(CCLParserCorpusTreeIter.java:7)
    at upparse.util.Pipe$1.getNext(Pipe.java:24)
    at upparse.util.PipeIterator.next(PipeIterator.java:20)
    at upparse.corpus.UnlabeledBracketSetCorpus.fromTreeIter(UnlabeledBracketSetCorpus.java:36)
    at upparse.corpus.CorpusUtil.cclpUnlabeledBracketSetCorpus(CorpusUtil.java:207)
    at upparse.cli.Main.getCCLParserOutput(Main.java:507)
    at upparse.cli.Main.cclpEval(Main.java:499)
    at upparse.cli.Main.main(Main.java:530)