[IO] Enhance bci2000 header parsing

Author: JuliaSprenger

neo/rawio/bci2000rawio.py

@@ -41,7 +41,7 @@ def _parse_header(self):
         sig_channels = []
         for chan_ix in range(file_info['SourceCh']):
             ch_name = param_defs['ChannelNames']['value'][chan_ix] \
-                if 'ChannelNames' in param_defs else 'ch' + str(chan_ix)
+                if 'ChannelNames' in param_defs and param_defs['ChannelNames']['value'] is not np.nan else 'ch' + str(chan_ix)
             chan_id = chan_ix + 1
             sr = param_defs['SamplingRate']['value']  # Hz
             dtype = file_info['DataFormat']