Protect against clusters that have no endpoints at all in the feature…

… walk.

Fixes #1532.

ambassador/ambassador/ir/ir.py

@@ -580,9 +580,16 @@ def features(self) -> Dict[str, Any]:
                 using_http = True
                 cluster_http_count += 1
 
-            cluster_endpoints = cluster.urls if (lb_type == 'kube') else cluster.targets
+            cluster_endpoints = cluster.urls if (lb_type == 'kube') else cluster.get('targets', [])
+
+            # Paranoia, really.
+            if not cluster_endpoints:
+                cluster_endpoints = []
+
             num_endpoints = len(cluster_endpoints)
 
+            # self.logger.debug(f'cluster {cluster.name}: lb_type {lb_type}, endpoints {cluster_endpoints} ({num_endpoints})')
+
             if using_tls:
                 endpoint_tls_count += num_endpoints