switch bug

```php
<?php
$a=10;
switch($a){
   case 10:
       echo "10\n";
   case 20:
       echo "20\n";
       break;
   default:
       echo "default\n";
}
```
expacted output
===

```
10
default
```
but got
===

```
10
20
```

here is a bug fix. ;)