[bugfix] Set a default value to the detection stepsize.

interekt.py

@@ -3834,6 +3834,7 @@ class Interekt:
 
         # Set the space step for skeleton detection process
         self.detection_step = Tk.DoubleVar()
+        self.detection_step.set(0.3)
         options_menu.add_command(label=_("Stepsize for skeleton detection"),
                                  command=detection_step_setting)
 

interekt_hdf5_store.py

@@ -669,6 +669,7 @@ def get_detection_step(hdf5file):
     Return the spatial step size (in pixels) used in the algorithm of
     skeleton detection.
     """
+    default_value = 0.3
     step = None
     with h5py.File(hdf5file, 'r') as f:
         if 'detection_step' in f:
@@ -676,6 +677,8 @@ def get_detection_step(hdf5file):
             if step == {}:
                 step = None
 
+    if step is None or not step:
+        step = default_value
     return step