errors when no channel specified
when zooming:
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/ndscope/scope.py", line 568, in update_mouse
self._data_request()
File "/usr/lib/python3/dist-packages/ndscope/scope.py", line 518, in _data_request
self.data.request(trend, (start, end))
File "/usr/lib/python3/dist-packages/ndscope/data.py", line 451, in request
dstart, dend = self.db[trend].range
File "/usr/lib/python3/dist-packages/ndscope/data.py", line 224, in range
return list(self.buffers.values())[0].range
IndexError: list index out of range