FIX: Do not show nested user cards. (#6621)

test/javascripts/acceptance/user-card-test.js.es6

@@ -1,4 +1,5 @@
 import { acceptance } from "helpers/qunit-helpers";
+import DiscourseURL from "discourse/lib/url";
 
 acceptance("User Card");
 
@@ -8,4 +9,8 @@ QUnit.test("user card", async assert => {
 
   await click("a[data-user-card=eviltrout]:first");
   assert.ok(visible("#user-card"), "card should appear");
+
+  sandbox.stub(DiscourseURL, "routeTo");
+  await click(".card-content a.mention");
+  assert.ok(DiscourseURL.routeTo.calledWith("/u/eviltrout"));
 });