fixed bug in ConcatenatedCorpusView that caused iteration to fail if it didn't start from the beginning of the corpus (e.g., somecorpusview[2000]).
fixed bug in ConcatenatedCorpusView that caused iteration to fail if it didn't start from the beginning of the corpus (e.g., somecorpusview[2000]).

svn/trunk@5624

nltk/nltk,nltk/nltk,nltk/nltk