Fix peak finding example

pycrystfel/bindings.pyx

@@ -72,8 +72,11 @@ def find_peaks_single_panel(cnp.ndarray[cnp.npy_float, ndim=2] data, str geom_fi
 
     df = featurelist_to_dataframe(image.features)
 
+    image.dp = NULL
     crystfel.image_free(image)
 
+    return df
+
 
 # Pointer wrapper machinery based on Cython docs:
 # https://cython.readthedocs.io/en/latest/src/userguide/extension_types.html#instantiation-from-existing-c-c-pointers