data stream: add method to iterate over stream data

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

@@ -49,6 +49,14 @@ class DataStream(BigFile):
                     , PropertySheet.SortIndex
                     )
 
+  def iterate(self, start_offset, end_offset):
+    """
+      Read chunks of data from a Data Stream and yield them.
+    """
+    data = self._baseGetData()
+    for chunk in data.iterate(start_offset, end_offset - start_offset):
+      yield chunk
+
   def readChunkList(self, start_offset, end_offset):
     """
       Read chunks of data from a Data Stream and return them.

bt5/erp5_wendelin/DocumentTemplateItem/portal_components/document.erp5.DataStream.xml

@@ -45,7 +45,9 @@
         <item>
             <key> <string>text_content_warning_message</string> </key>
             <value>
-              <tuple/>
+              <tuple>
+                <string>W: 71,  2: Arguments number differs from overridden \'appendData\' method (arguments-differ)</string>
+              </tuple>
             </value>
         </item>
         <item>