Update Tatoeba-Challenge-v2021-08-07-ja-zh.py

Tatoeba-Challenge-v2021-08-07-ja-zh.py

@@ -162,5 +162,5 @@ class tatoebaMT(datasets.GeneratorBasedBuilder):
                     "sourceLang": 'ja',
                     "targetlang": 'zh_cn',
                     "sourceString": row[0],
-                    "targetString": row[1]
+                    "targetString": row[1] if len(row) > 1 else ""
                 }