Word2VecModel.findSynonyms can spuriously reject the best match when invoked with a vector

The `findSynonyms` method in `Word2VecModel` currently rejects the best match a priori. When `findSynonyms` is invoked with a word, the best match is almost certain to be that word, but `findSynonyms` can also be invoked with a vector, which might not correspond to any of the words in the model's vocabulary. In the latter case, rejecting the best match is spurious.