Data Bucket Stream: add method getKeyByIndex

bt5/erp5_wendelin/DocumentTemplateItem/portal_components/document.erp5.DataBucketStream.py

@@ -265,6 +265,12 @@ class DataBucketStream(Document):
     key = self._long_index_tree[index]
     return self.getBucketByKey(key).value
 
+  def getKeyByIndex(self, index):
+    """
+      Get the bucket key by a given index
+    """
+    return self._long_index_tree[index]
+    
   def hasBucketKey(self, key):
     """
       Wether bucket with such key exists