Revert "Update reference body again"

This reverts commit a38c6ec551.

poezio_omemo/__init__.py

@@ -149,7 +149,7 @@ class Plugin(E2EEPlugin):
             )
             # Heartbeats will return a None body.
             if body is not None:
-                message['body'] = body.decode('utf-8')
+                body = body.decode('utf-8')
         except (MissingOwnKey,):
             # The message is missing our own key, it was not encrypted for
             # us, and we can't decrypt it.
@@ -181,7 +181,8 @@ class Plugin(E2EEPlugin):
             self.display_error(f'An error occured while attempting decryption.\n{exn}')
             raise
 
-        return None
+        if body is not None:
+            message['body'] = body
 
     async def encrypt(self, message: Message, jids: Optional[List[JID]], _tab) -> None:
         if jids is None: