Fix boundary condition in token_block_utils_fast.pyx (facebookresearc…

…h#1445)

Summary:
In cases where the item size in the underlying dataset is 0, it's possible that `remaining` is initialized to 0. We can update the assert to reflect this.

Pull Request resolved: fairinternal/fairseq-py#1445

Reviewed By: alexeib

Differential Revision: D25054723

Pulled By: myleott

fbshipit-source-id: 1bb73cce34e973f407436c442b698ce706d97359

fairseq/data/token_block_utils_fast.pyx

@@ -170,7 +170,7 @@ cdef class DatasetSearcher(object):
                 self.current_offset += to_consume
                 self.current_i += to_consume
             else:
-                assert remaining > 0
+                assert remaining >= 0
                 self.current_i += remaining
                 self.current_index += 1
                 self.current_offset = 0