Fix googleapis#302 again. Missed the initial check

Author: Alejandro Casanovas

O365/mailbox.py

@@ -142,8 +142,8 @@ def get_message(self, object_id=None, query=None, *, download_attachments=False)
         :return: one Message
         :rtype: Message or None
         """
-        if object_id is not None and query is not None:
-            raise ValueError('Must provide object id or query but not both.')
+        if object_id is None and query is None:
+            raise ValueError('Must provide object id or query.')
 
         if object_id is not None:
             url = self.build_url(self._endpoints.get('message').format(id=object_id))