call ajax scan only if a user is logged in - otherwise we'll get a 500

apps/files/js/files.js

@@ -776,6 +776,10 @@ $(document).ready(function() {
 });
 
 function scanFiles(force, dir){
+	if (!OC.currentUser) {
+		return;
+	}
+
 	if(!dir){
 		dir = '';
 	}