bt5/erp5_wendelin/DataBucketStream: Fix getBucketByIndex

Before this patch 'getBucketByIndex' was buggy & would fail with

    AttributeError: 'str' object has no attribute 'value'

But it wasn't recognized, because this method wasn't tested before. This
patch adds a test to the method & fixes it.

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

@@ -206,7 +206,7 @@ class DataBucketStream(Document):
       Get one bucket
     """
     key = self._long_index_tree[index]
-    return self.getBucketByKey(key).value
+    return self.getBucketByKey(key)
 
   def getKeyByIndex(self, index):
     """
@@ -432,4 +432,4 @@ for index_class in (
   ContainerAssertions[index_class] = 1
 
 # Cleanup
-del index_class
+del index_class
\ No newline at end of file

bt5/erp5_wendelin/TestTemplateItem/portal_components/test.erp5.testWendelin.py

@@ -261,6 +261,7 @@ class Test(ERP5TypeTestCase):
     key = len(bucket_stream) + 1
     bucket_stream.insertBucket(key, bin_string )
     self.assertEqual(bin_string, bucket_stream.getBucketByKey(key))
+    self.assertEqual(bin_string, bucket_stream.getBucketByIndex(0))
 
     # test sequence
     self.assertEqual(1, len(bucket_stream))