Revert 738272f and reimplement hide graph link

commit 738272f to hide Mantisgraph link
introduced a regression: failing at login when anonymous login is
disabled.

Here that change is reverted and the access level check is now placed in
the callback function, instead of the hook initialization

Fixes #20217

Signed-off-by: Damien Regad <dregad@mantisbt.org>

plugins/MantisGraph/MantisGraph.php

@@ -87,10 +87,8 @@ function hooks() {
 		$t_hooks = array(
 			'EVENT_MENU_SUMMARY' => 'summary_menu',
 			'EVENT_SUBMENU_SUMMARY' => 'summary_submenu',
+			'EVENT_MENU_FILTER' => 'graph_filter_menu'
 		);
-		if( access_has_project_level( config_get( 'view_summary_threshold' ) ) ) {
-			$t_hooks['EVENT_MENU_FILTER'] = 'graph_filter_menu';
-		}
 		return $t_hooks;
 	}
 
@@ -107,7 +105,11 @@ function summary_menu() {
 	 * @return array
 	 */
 	function graph_filter_menu() {
-		return array( '<a href="' . plugin_page( 'bug_graph_page.php' ) . '">' . plugin_lang_get( 'graph_bug_page_link' ) . '</a>', );
+		if( access_has_project_level( config_get( 'view_summary_threshold' ) ) ) {
+			return array( '<a href="' . plugin_page( 'bug_graph_page.php' ) . '">' . plugin_lang_get( 'graph_bug_page_link' ) . '</a>', );
+		} else {
+			return '';
+		}
 	}
 
 	/**