sideview crashes in stable when no markers are drawn

[joernu76]

Traceback (most recent call last):
  File "/home/ahk/.pixi/envs/mss/lib/python3.11/site-packages/matplotlib/markers.py", line 326, in _set_marker
    Path(marker)
  File "/home/ahk/.pixi/envs/mss/lib/python3.11/site-packages/matplotlib/path.py", line 130, in __init__
    _api.check_shape((None, 2), vertices=vertices)
  File "/home/ahk/.pixi/envs/mss/lib/python3.11/site-packages/matplotlib/_api/__init__.py", line 161, in check_shape
    raise ValueError(
ValueError: 'vertices' must be 2D with shape (N, 2), but your input has shape ()

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/ahk/.pixi/envs/mss/lib/python3.11/site-packages/mslib/msui/msui_mainwindow.py", line 924, in create_view_handler
    self.create_view(_type, self.mscolab.waypoints_model)
  File "/home/ahk/.pixi/envs/mss/lib/python3.11/site-packages/mslib/msui/msui_mainwindow.py", line 949, in create_view
    view_window = sideview.MSUISideViewWindow(mainwindow=self, model=model, tutorial_mode=self.tutorial_mode,
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ahk/.pixi/envs/mss/lib/python3.11/site-packages/mslib/msui/sideview.py", line 308, in __init__
    self.setFlightTrackModel(model)
  File "/home/ahk/.pixi/envs/mss/lib/python3.11/site-packages/mslib/msui/sideview.py", line 424, in setFlightTrackModel
    super().setFlightTrackModel(model)
  File "/home/ahk/.pixi/envs/mss/lib/python3.11/site-packages/mslib/msui/viewwindows.py", line 273, in setFlightTrackModel
    self.mpl.canvas.set_waypoints_model(model)
  File "/home/ahk/.pixi/envs/mss/lib/python3.11/site-packages/mslib/msui/mpl_qtwidget.py", line 1234, in set_waypoints_model
    self.set_settings(None)
  File "/home/ahk/.pixi/envs/mss/lib/python3.11/site-packages/mslib/msui/mpl_qtwidget.py", line 1349, in set_settings
    wpi_plotter.line.set_marker("o" if settings["draw_marker"] else None)
  File "/home/ahk/.pixi/envs/mss/lib/python3.11/site-packages/matplotlib/lines.py", line 1199, in set_marker
    self._marker = MarkerStyle(marker, self._marker.get_fillstyle())
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ahk/.pixi/envs/mss/lib/python3.11/site-packages/matplotlib/markers.py", line 248, in __init__
    self._set_marker(marker)
  File "/home/ahk/.pixi/envs/mss/lib/python3.11/site-packages/matplotlib/markers.py", line 329, in _set_marker
    raise ValueError(
ValueError: Unrecognized marker style None

Seemingly matplotlib had an API change. Instead of None it should be "" now.

[ReimarBauer]

fixed with #2678