assign a default value to groupless channels

Author: h-mayorquin

neo/rawio/neuroscoperawio.py

@@ -69,11 +69,12 @@ def _parse_header(self):
 
         # one unique stream
         signal_streams = np.array([('Signals', '0')], dtype=_signal_stream_dtype)
-
+        
         # signals
         sig_channels = []
         for c in range(nb_channel):
-            name = 'ch{}grp{}'.format(c, channel_group[c])
+            name = 'ch{}grp{}'.format(c, channel_group.get(c, 'none'))
+ 
             chan_id = str(c)
             units = 'mV'
             offset = 0.