Fix leak on double DatePeriod::__construct() call

[iluuu1994]

See https://github.com/php/php-src/actions/runs/28911263674/job/85769105449.

Normally we might want to discuss whether such code is even sensible, but it seems carbon is relying on it, as evidenced by the CI failure above. A minimal carbon example that reproduces the error:

<?php

use Carbon\Carbon;

require __DIR__ . '/vendor/autoload.php';

$day = Carbon::now();
$period = Carbon::now()->toPeriod($day);

Just remembered, will have to rebase onto 8.2 to keep nightly green.

[TimWolla]

Just looked at the diff, didn't check for completeness. I trust you there.

[TimWolla]

Suggested change

	memset(period_obj, 0, XtOffsetOf(php_period_obj, std));
	memset(period_obj, 0, offsetof(php_period_obj, std));

We only removed XtOffsetOf with 8.6, but offsetof() is reliably available even for 8.4.

[iluuu1994]

I remembered your change. Will have to be backported to 8.2, so I'd prefer just changing on master to match your other PR.

[iluuu1994]

@kylekatarnls I hope it's ok to ping you directly. Just wanted to check with you whether the double constructor call is even intentional. This issue popped up recently in our CI, so I figured it might not be.