check file existance before autoloading

Even for our own namespace, file existance should be checked before
attempting to load it. Otherwise class_exist() check will throw errors.

inc/load.php

@@ -135,8 +135,11 @@ function load_autoload($name){
 
     // our own namespace
     if(substr($name, 0, 9) == 'dokuwiki/') {
-        require substr($name, 9) . '.php';
-        return true;
+        $file = DOKU_INC . 'inc/'. substr($name, 9) . '.php';
+        if(file_exists($file)) {
+            require $file;
+            return true;
+        }
     }
 
     // Plugin loading