Bug fix, first position is always 1

src/ERP5Diff.py

@@ -456,7 +456,7 @@ class ERP5Diff:
         len_all_similar_sibling = len(element.findall('../%s' % element.tag))
         if len_all_similar_sibling > 1:
           position = len_all_similar_sibling - len(list(element.itersiblings(tag=element.tag)))
-          path_list.append('%s[%d]' % (element.xpath('name()'), position-before))
+          path_list.append('%s[%d]' % (element.xpath('name()'), position-before or 1))
         else:
           path_list.append(element.xpath('name()'))