fix bug

Author: anla-xu

pymycobot/mercury.py

@@ -165,6 +165,7 @@ def _mesg(self, genre, *args, **kwargs):
                                 for j in range(16):
                                     if data[j] != "0":
                                         res[i].append(15-j)
+                        return res
                 else:
                     return res
             return None