Description:
------------
When use "pcntl_async_signals(true)" and try to access the magic property from async signal handler and regular way in same time, get error "Undefined property". 

PHP 7.1 7.2 7.3:
docker run -it --rm -v "$PWD":/app php:7.1.29-cli sh -c "docker-php-ext-install -j"$(getconf _NPROCESSORS_ONLN)" pcntl && php /app/test-magic.php"
docker run -it --rm -v "$PWD":/app php:7.2.18-cli sh -c "docker-php-ext-install -j"$(getconf _NPROCESSORS_ONLN)" pcntl && php /app/test-magic.php"
docker run -it --rm -v "$PWD":/app php:7.3.5-cli sh -c "docker-php-ext-install -j"$(getconf _NPROCESSORS_ONLN)" pcntl && php /app/test-magic.php"

Test script:
---------------
<?php //test-magic.php
$obj = new TestMagic;
$childrenCount = 100;
$completed = 0;

pcntl_async_signals(true);

set_error_handler(static function (int $errNo, string $errStr) {
    throw new \ErrorException("ERROR #{$errNo}: {$errStr}");
});

pcntl_signal(SIGINT, static function () {exit;});
pcntl_signal(SIGTERM, static function () {exit;});
pcntl_signal(SIGCHLD, static function () use ($obj, &$completed) {
    $completed++;
    echo "ASYNC ACCESS #{$completed} ";
    echo "{$obj->x}\n";
});

$inRun = 0;
while (++$inRun <= $childrenCount) {
    proc_open('sleep ' . (random_int(1, 999) / 1000), [['pipe', 'r'], ['pipe', 'w'], ['pipe', 'w']], $pipes);
}

while ($completed < $childrenCount) {
    echo "BLOCKING ACCESS #{$completed} ";
    echo "{$obj->x}\n";
}

/** @property $x */
class TestMagic
{
    public function __set($name, $value)
    {
        return null;
    }

    public function __get($name)
    {
        return 'OK';
    }

    public function __isset($name)
    {
        return true;
    }
}

// ...
// BLOCKING ACCESS #5 OK
// BLOCKING ACCESS #5 ASYNC ACCESS #6 
// Fatal error: Uncaught ErrorException: ERROR #8: Undefined property: TestMagic::$x in /app/test-magic.php:9
// Stack trace:
// #0 /app/test-magic.php(17): {closure}(8, 'Undefined prope...', '/app/test-magic...', 17, Array)
// #1 /app/test-magic.php(41): {closure}(17, Array)
// #2 /app/test-magic.php(27): TestMagic->__get('x')
// #3 {main}
//   thrown in /app/test-magic.php on line 9
// Segmentation fault (core dumped)