don't error if federation query doesn't have cross-signing keys

synapse/handlers/e2e_keys.py

@@ -218,13 +218,15 @@ class E2eKeysHandler(object):
                     if user_id in destination_query:
                         results[user_id] = keys
 
-                for user_id, key in remote_result["master_keys"].items():
-                    if user_id in destination_query:
-                        cross_signing_keys["master_keys"][user_id] = key
-
-                for user_id, key in remote_result["self_signing_keys"].items():
-                    if user_id in destination_query:
-                        cross_signing_keys["self_signing_keys"][user_id] = key
+                if "master_keys" in remote_result:
+                    for user_id, key in remote_result["master_keys"].items():
+                        if user_id in destination_query:
+                            cross_signing_keys["master_keys"][user_id] = key
+
+                if "self_signing_keys" in remote_result:
+                    for user_id, key in remote_result["self_signing_keys"].items():
+                        if user_id in destination_query:
+                            cross_signing_keys["self_signing_keys"][user_id] = key
 
             except Exception as e:
                 failure = _exception_to_failure(e)