Description:
------------
calling unary increment operator (++) on unset overloaded member variable leaves variable unset instead of setting it to 1


Reproduce code:
---------------
<?php
class A {
	public $v;
}
class B {
	private $data;
	public function __set ($name, $value) {
		$data[$name] = $value;
	}
	public function __get ($name) {
		return $data[$name];
	}
}
$a = new A ();
$b = new B ();
$a->v++;
$b->v++;
echo "\$a->v is: {$a->v}<br/>";
echo "\$b->v is: {$b->v}<br/>";
?>

Expected result:
----------------
$a->v is: 1
$b->v is: 1

Actual result:
--------------
$a->v is: 1
$b->v is: