text: Title: masking function in multifit(mask) does not work as expected
  Body: Dear all,
  
  I would like to use the multifit function with a mask (see below). Unfortunately I get a ValueError message that makes no sense for me. Do I something wrong? Is there a workaround or a similar solution for my problem?
  
  Thanks a lot!
  
  
  ```
  s = hs.load("datasets/PS71-T_0013.dm3")
  print(s.axes_manager)
  
  <Axes manager, axes: (|512)>
       Name |   size |  index |  offset |   scale |  units 
  ================ | ====== | ====== | ======= | ======= | ====== 
  ---------------- | ------ | ------ | ------- | ------- | ------ 
       Energy loss |    512 |        | 5.4e+02 |     0.8 |     eV 
  
  ```
  
  
  
  
  `m = s.create_model()`
  
  
  
  
  
  ```
  m.components
  
      |      Attribute Name |      Component Name |      Component Type
  ---- | ------------------- | ------------------- | -------------------
     0 |            PowerLaw |            PowerLaw |            PowerLaw
     1 |               Ni_L3 |               Ni_L3 |          EELSCLEdge
     2 |               Fe_L3 |               Fe_L3 |          EELSCLEdge
  ```
  
  
  
  
  
  ```
  m.axes_manager._navigation_shape_in_array
  
  ()
  ```
  
  
  
  
  ```
  mask = np.ones((1,512)).astype(bool)
  mask[:,0:66] = False
  mask[:,486:512] = False
  mask.dtype
  
  dtype('bool')
  ```
  
  
  
  
  ```
  m.multifit(mask=mask, kind='smart')
  
  ---------------------------------------------------------------------------
  ValueError                                Traceback (most recent call last)
  Input In [273], in <module>
  ----> 1 m.multifit(mask=mask, kind='smart')
  
  File D:\Anaconda\envs\hyperspy-eels\lib\site-packages\hyperspy\model.py:1569, in BaseModel.multifit(self, mask, fetch_only_fixed, autosave, autosave_every, show_progressbar, interactive_plot, iterpath, **kwargs)
     1561     _logger.info(
     1562         f"Autosaving every {autosave_every} pixels to {autosave_fn}.npz. "
     1563         "When multifit finishes, this file will be deleted."
     1564     )
     1566 if mask is not None and (
     1567     mask.shape != tuple(self.axes_manager._navigation_shape_in_array)
     1568 ):
  -> 1569     raise ValueError(
     1570         "The mask must be a numpy array of boolean type with "
     1571         f"shape: {self.axes_manager._navigation_shape_in_array}"
     1572     )
     1574 masked_elements = 0 if mask is None else mask.sum()
     1575 maxval = self.axes_manager.navigation_size - masked_elements
  
  ValueError: The mask must be a numpy array of boolean type with shape: ()
  ```
  