Description:
------------
An invalid array offset will trigger a TypeError when used in isset/empty.

The same should be done for string offsets.

Test script:
---------------
<?php

$s = 'Hello';
$o = new stdClass();
$a = [];

try {
    var_dump(isset($s[$o]));
} catch (\Throwable $e) {
    echo $e->getMessage(), "\n";
}
try {
    var_dump(empty($s[$o]));
} catch (\Throwable $e) {
    echo $e->getMessage(), "\n";
}
try {
    var_dump(isset($s[$a]));
} catch (\Throwable $e) {
    echo $e->getMessage(), "\n";
}
try {
    var_dump(empty($s[$a]));
} catch (\Throwable $e) {
    echo $e->getMessage(), "\n";
}
try {
    var_dump(isset($s[[]]));
} catch (\Throwable $e) {
    echo $e->getMessage(), "\n";
}
try {
    var_dump(empty($s[[]]));
} catch (\Throwable $e) {
    echo $e->getMessage(), "\n";
}

?>