fix loading dicom of 2D images

mu_map/file/dicom.py

@@ -145,7 +145,12 @@ def to_direction(
     :return: dicom header (with values updated) and image according to the desired stacking order
     """
     dcm, image = dcm
-    spacing_between_slices = float(dcm.SpacingBetweenSlices)
+
+    try:
+        spacing_between_slices = float(dcm.SpacingBetweenSlices)
+    except AttributeError:
+        return dcm, image
+
     if spacing_between_slices * direction < 0:
         dcm.DetectorInformationSequence[0].ImagePositionPatient[2] *= (
             image.shape[0] * spacing_between_slices