muted_topics: Rerender list only if modal is opened and section is loaded.

We should rernder the muted topics list in settings only if the settings
modal is opened and the muted topics section is loaded.

static/js/settings_sections.js

@@ -77,6 +77,7 @@ exports.reset_sections = function () {
     settings_profile_fields.reset();
     settings_streams.reset();
     settings_user_groups.reset();
+    settings_muting.reset();
     // settings_users doesn't need a reset()
 };