fix the issue michiya#158

Author: michiya

sql_server/pyodbc/compiler.py

@@ -78,7 +78,7 @@ def _cursor_iter(cursor, sentinel, col_count):
     Yields blocks of rows from a cursor and ensures the cursor is closed when
     done.
     """
-    if cursor.db.supports_mars:
+    if not hasattr(cursor.db, 'supports_mars') or cursor.db.supports_mars:
         # same as the original Django implementation
         try:
             for rows in iter((lambda: cursor.fetchmany(GET_ITERATOR_CHUNK_SIZE)),