Description:
------------
pgsqlGetNotify() doesn't check the result of PQconsumeInput(),
which returns 0 on error.
If a caller is pooling by calling pgsqlGetNotify(),
it will never have a chance to known when the connection is lost.

(will add a PR)

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

$connArgs = ['pgsql:dbname=DB_NAME', 'USER', 'PASSWORD', [
    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
]];
$pdo = new PDO(...$connArgs);
$pdo->exec('listen "test-event"');

var_dump($pdo->pgsqlGetNotify(PDO::FETCH_NUM, 1000));

sleep(15); // kill the DB connection here
//system('sudo systemctl restart postgresql-12');
//system('net stop postgresql-x64-12 && net start postgresql-x64-12');

var_dump($pdo->pgsqlGetNotify(PDO::FETCH_NUM, 1000)); // should throw but doesn't
var_dump($pdo->query('select 1')); // throws


Expected result:
----------------
throws on $pdo->pgsqlGetNotify()

Actual result:
--------------
throws after $pdo->pgsqlGetNotify(), on $pdo->query('select 1')