auth-token: only delete token if it exists.

rhodecode/model/auth_token.py

@@ -71,6 +71,8 b' class AuthTokenModel(BaseModel):'
             user = self._get_user(user)
             auth_token = auth_token.filter(UserApiKeys.user_id == user.user_id)
             auth_token = auth_token.scalar()
+
+        if auth_token:
         try:
             Session().delete(auth_token)
         except Exception: