Fix full screen mode for snippet comments

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 7.14.0 (unreleased)
+  - Fix full screen mode for snippet comments (Daniel Gerhardt)
   - Fix label read access for unauthenticated users (Daniel Gerhardt)
   - Fix access to disabled features for unauthenticated users (Daniel Gerhardt)
   - Fix OAuth provider bug where GitLab would not go return to the redirect_uri after sign-in (Stan Hu)

app/assets/javascripts/dispatcher.js.coffee

@@ -128,7 +128,10 @@ class Dispatcher
             shortcut_handler = new ShortcutsNavigation()
             new ZenMode()
             new DropzoneInput($('.wiki-form'))
-          when 'snippets', 'labels', 'graphs'
+          when 'snippets'
+            shortcut_handler = new ShortcutsNavigation()
+            new ZenMode() if path[2] == 'show'
+          when 'labels', 'graphs'
             shortcut_handler = new ShortcutsNavigation()
           when 'project_members', 'deploy_keys', 'hooks', 'services', 'protected_branches'
             shortcut_handler = new ShortcutsNavigation()