FIX: Selecting & moving posts not working on megatopics.

test/javascripts/acceptance/topic-test.js.es6

@@ -252,6 +252,11 @@ QUnit.test("selecting posts", async assert => {
     "it should show the multi select menu"
   );
 
+  assert.ok(
+    exists(".select-all"),
+    "it should allow users to select all the posts"
+  );
+
   await click(".toggle-admin-menu");
 
   assert.ok(

test/javascripts/controllers/topic-test.js.es6

@@ -123,6 +123,16 @@ QUnit.test("selectedAllPosts", function(assert) {
     controller.get("selectedAllPosts"),
     "all posts (including filtered posts) are selected"
   );
+
+  model.setProperties({
+    "postStream.isMegaTopic": true,
+    posts_count: 1
+  });
+
+  assert.ok(
+    controller.get("selectedAllPosts"),
+    "it uses the topic's post count for megatopics"
+  );
 });
 
 QUnit.test("selectedPostsUsername", function(assert) {