support bpe tokenizer in convert

Signed-off-by: ldwang <ftgreat@gmail.com>

convert.py

@@ -242,10 +242,6 @@ class SentencePieceVocab:
           byte_decoder = {v: k for k, v in byte_encoder.items()}
           for i, item in enumerate(tokenizer):
             text: bytes
-            if i == 0:
-                text = " \u2047 ".encode("utf-8")
-                score = 0.0
-            else:
             text = b''.join([x.to_bytes(1, byteorder='big') for x in [byte_decoder[y] for y in item]])
             score: float = -i
             yield text, score