fix bug for async written error

Author: Germey

acedatacloud_scaffold/__version__.py

@@ -1,3 +1,3 @@
-VERSION = (0, 7, 4)
+VERSION = (0, 7, 5)
 
 __version__ = '.'.join(map(str, VERSION))

acedatacloud_scaffold/handlers/callback.py

@@ -33,6 +33,9 @@ def write_index(self):
         })
         self.finish()
         self._finished = False
+        # this flag used for checking if headers has been written,
+        # if headers not written, we can continue return error sync
+        self._headers_written = False
         # this flag used for checking if index has been written,
         # if index not written, we can return error sync
         self.index_written = True