Fix crash when changing the location of app with disabled sendmail addon

src/apps.js

@@ -1655,7 +1655,7 @@ async function setLocation(app, data, auditSource) {
     }
 
     // rename the auto-created mailbox to match the new location
-    if (app.manifest.addons?.sendmail && app.mailboxName.endsWith('.app')) {
+    if (app.manifest.addons?.sendmail && app.mailboxName?.endsWith('.app')) {
         values.mailboxName = mailboxNameForLocation(values.location, app.manifest);
         values.mailboxDomain = values.domain;
     }