[odrs-web] Fix a backtrace seen when merging components

[Richard Hughes <rhughes src gnome org>]

commit 999dd01f9049da909675d2c1dfa136583738c11e
Author: Richard Hughes <richard hughsie com>
Date:   Fri Jul 5 13:42:09 2019 +0100

    Fix a backtrace seen when merging components

 app_data/odrs/models.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/app_data/odrs/models.py b/app_data/odrs/models.py
index 8103c99..bcac095 100644
--- a/app_data/odrs/models.py
+++ b/app_data/odrs/models.py
@@ -274,9 +274,10 @@ class Review(db.Model):
             'review_id': self.review_id,
             'summary': self.summary,
             'user_display': self.user_display,
-            'user_hash': self.user.user_hash,
             'version': self.version,
         }
+        if self.user:
+            item['user_hash'] = self.user.user_hash
         if user_hash:
             item['user_skey'] = _get_user_key(user_hash, self.component.app_id)
         return item