Fixed VarDumpOptimizer support variable-length arguments, compatible for...

Fixed VarDumpOptimizer support variable-length arguments, compatible for userland PHP 'var_dump' function.

ex:
``` 
var_dump(1.3, true, array(1,2,3), 'foo', 'bar');
```

Signed-off-by: Rack Lin <racklin@gmail.com>