Internal: avoid exception by initializing visibility variable in tool visibility in sessions

Author: juancp-contidosdixitais

main/inc/lib/course_home.lib.php

@@ -1866,6 +1866,7 @@ public static function getToolVisibility($toolName, $courseId, $sessionId = 0)
             );
         }
 
+        $visibility = false;
         if ($tool) {
             $visibility = $tool->getVisibility();
         }