[fix] crash when sentences no polyphonic words

Author: GitYCC

g2pw/api.py

@@ -149,6 +149,9 @@ def __call__(self, sentences):
             sentences = translated_sentences
 
         texts, query_ids, sent_ids, partial_results = self._prepare_data(sentences)
+        if len(texts) == 0:
+            # sentences no polyphonic words
+            return partial_results
 
         dataset = TextDataset(self.tokenizer, self.labels, self.char2phonemes, self.chars, texts, query_ids,
                               use_mask=self.config.use_mask, use_char_phoneme=self.config.use_char_phoneme,