fixes link for anonymous.png, a=chris

diff --git a/src/controllers/components/SocialComponent.php b/src/controllers/components/SocialComponent.php
index 9cffebf59..afcf62744 100644
--- a/src/controllers/components/SocialComponent.php
+++ b/src/controllers/components/SocialComponent.php
@@ -1091,7 +1091,7 @@ class SocialComponent extends Component implements CrawlConstants
             $pages = [];
             foreach ($groups as $group) {
                 $page = [];
-                $page['USER_ICON'] = "resources/anonymous.png";
+                $page['USER_ICON'] = C\BASE_URL . "resources/anonymous.png";
                 $page[self::TITLE] = tl('social_component_join_group',
                     $username, $group['GROUP_NAME']);
                 $page[self::DESCRIPTION] =