MDL-82359 Install: Change default for navadduserpostslinks if no forum

If forum is not available, there are debug warnings due to missing
language strings on every page while logged in, unless the
'navadduserpostslinks' setting is turned off. By default this setting
is on.

This change makes the default be on if forum is present (as current),
but off if it is not.

This change is a minimal workaround so that Moodle does not give errors
on every page and we can at least run some Behat tests.

admin/settings/appearance.php

@@ -182,7 +182,11 @@
     $temp->add(new admin_setting_configcheckbox('usesitenameforsitepages', new lang_string('usesitenameforsitepages', 'admin'), new lang_string('configusesitenameforsitepages', 'admin'), 0));
     $temp->add(new admin_setting_configcheckbox('linkadmincategories', new lang_string('linkadmincategories', 'admin'), new lang_string('linkadmincategories_help', 'admin'), 1));
     $temp->add(new admin_setting_configcheckbox('navshowfrontpagemods', new lang_string('navshowfrontpagemods', 'admin'), new lang_string('navshowfrontpagemods_help', 'admin'), 1));
-    $temp->add(new admin_setting_configcheckbox('navadduserpostslinks', new lang_string('navadduserpostslinks', 'admin'), new lang_string('navadduserpostslinks_help', 'admin'), 1));
+    // The navadduserpostslinks causes warnings on every page if forum is not present, so we will
+    // default to false if forum has been removed.
+    $temp->add(new admin_setting_configcheckbox('navadduserpostslinks',
+        new lang_string('navadduserpostslinks', 'admin'), new lang_string('navadduserpostslinks_help', 'admin'),
+        \core_component::get_component_directory('mod_forum') !== null));
 
     $ADMIN->add('appearance', $temp);