allow initializing when slice axis is pixel

jdaviz/configs/cubeviz/plugins/slice/slice.py

@@ -97,7 +97,7 @@ def __init__(self, *args, **kwargs):
         self._initialize_location()
 
     def _initialize_location(self, *args):
-        # intitialize value_unit (this has to wait until data is loaded to an existing
+        # initialize value_unit (this has to wait until data is loaded to an existing
         # slice_indicator_viewer, so we'll keep trying until it is set - after that, changes
         # will be handled by a change to global display units)
         if not self.value_unit:
@@ -133,7 +133,7 @@ def slice_axis(self):
 
     @property
     def valid_slice_att_names(self):
-        return _spectral_axis_names
+        return _spectral_axis_names + ['Pixel Axis 2 [x]']
 
     @property
     def slice_selection_viewers(self):

jdaviz/configs/cubeviz/plugins/viewers.py

@@ -43,7 +43,8 @@ def _get_component(layer):
                 # either way, return an empty array and skip this layer
                 return np.array([])
         try:
-            return np.asarray(np.unique(np.concatenate([_get_component(layer) for layer in self.layers])), dtype=float)
+            return np.asarray(np.unique(np.concatenate([_get_component(layer) for layer in self.layers])),  # noqa
+                              dtype=float)
         except ValueError:
             return np.array([])