Stop animation before switching plot method

[Chilipp]

When running a animation and changing the plot method, psy-view crashes, see the following screencast

The error message in the terminal is

Traceback (most recent call last):
  File "/home/psommer/miniconda3/envs/work/lib/python3.7/site-packages/matplotlib/backend_bases.py", line 1187, in _on_timer
    ret = func(*args, **kwargs)
  File "/home/psommer/miniconda3/envs/work/lib/python3.7/site-packages/matplotlib/animation.py", line 1449, in _step
    still_going = Animation._step(self, *args)
  File "/home/psommer/miniconda3/envs/work/lib/python3.7/site-packages/matplotlib/animation.py", line 1168, in _step
    framedata = next(self.frame_seq)
  File "/home/psommer/miniconda3/envs/work/lib/python3.7/site-packages/matplotlib/animation.py", line 1672, in iter_frames
    yield from this
  File "/home/psommer/Documents/code/development/psy-view/psy_view/ds_widget.py", line 418, in animation_frames
    i = self.data.psy.idims[dim]
  File "/home/psommer/Documents/code/development/psy-view/psy_view/ds_widget.py", line 604, in data
    return self.plotmethod_widget.data
  File "/home/psommer/Documents/code/development/psy-view/psy_view/ds_widget.py", line 865, in data
    return self.sp[0]
  File "/home/psommer/Documents/code/development/psyplot/psyplot/project.py", line 637, in __getitem__
    ret = super(Project, self).__getitem__(key)
  File "/home/psommer/Documents/code/development/psyplot/psyplot/data.py", line 4477, in __getitem__
    return super(ArrayList, self).__getitem__(key)
IndexError: list index out of range
Aborted (core dumped)