Fix uninitialized magnified_size

tomoscan/esrf/hdf5scan.py

@@ -158,6 +158,8 @@ class HDF5TomoScan(TomoScanBase):
         # image dimensions
         self._x_pixel_size = None
         self._y_pixel_size = None
+        self._x_magnified_pixel_size = None
+        self._y_magnified_pixel_size = None
         # pixel dimensions (tuple)
         self._frames = None
         self._image_keys = None