dballe.Message.query_data() error when the BUFR has only station data

[edigiacomo]

In [4]: import dballe

In [5]: importer = dballe.Importer("BUFR") 
   ...: with importer.from_file("tmp/rotto.bufr") as f: 
   ...:     for msgs in f: 
   ...:         for msg in msgs: 
   ...:             for d in msg.query_data(): 
   ...:                 print(d["trange"]) 
   ...:                                                                                                                                                                                                                                       
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-5-432d121cea6f> in <module>
      4         for msg in msgs:
      5             for d in msg.query_data():
----> 6                 print(d["trange"])
      7 

RuntimeError: cannot access values on a cursor before or after iteration

Test file: rotto.zip