Add try/catch clause for sentences with large number of wordpieces.

Add try/catch clause for sentences with large number of wordpieces.

combo/data/token_indexers/pretrained_transformer_mismatched_indexer.py

@@ -4,8 +4,6 @@ from allennlp import data
 from allennlp.data import token_indexers, tokenizers, IndexedTokenList, vocabulary
 from overrides import overrides
 
-from typing import List
-
 
 @data.TokenIndexer.register("pretrained_transformer_mismatched_fixed")
 class PretrainedTransformerMismatchedIndexer(token_indexers.PretrainedTransformerMismatchedIndexer):