Fix Expose page crash when filtered by assistant

The assistants URL filter can skip creating a row for entities that are
only exposed via Cloud (Alexa/Google) manual config, but the sortable key
was still assigned to the missing row, throwing a TypeError and leaving
the page on an infinite spinner. Only assign the key when the row exists.

Fixes #53689

Author: maartenla

src/panels/config/voice-assistants/ha-config-voice-assistants-expose.ts

@@ -395,9 +395,11 @@ export class VoiceAssistantsExpose extends LitElement {
               aliases: entry?.aliases || [],
             };
           }
-          result[entityId].assistants_sortable_key = getAssistantsSortableKey(
-            result[entityId].assistants
-          );
+          if (result[entityId]) {
+            result[entityId].assistants_sortable_key = getAssistantsSortableKey(
+              result[entityId].assistants
+            );
+          }
         });
       }
       return Object.values(result);