ext/pdo_pgsql: Fix crash when a persistent connection fails

The shutdown function tried to reset the session state even when the
connection had failed.

Regression from GH-20572.

Author: KentarouTakeda

ext/pdo_pgsql/pgsql_driver.c

@@ -1397,7 +1397,7 @@ static void pdo_pgsql_request_shutdown(pdo_dbh_t *dbh)
 	PGresult *res;
 	pdo_pgsql_db_handle *H = (pdo_pgsql_db_handle *)dbh->driver_data;
 
-	if(H->server) {
+	if(H && H->server) {
 		res = PQexec(H->server, "DISCARD ALL");
 
 		if(res) {

ext/pdo_pgsql/tests/persistent_connection_failure.phpt

@@ -0,0 +1,21 @@
+--TEST--
+PDO PgSQL failed persistent connection does not crash on object destruction
+--EXTENSIONS--
+pdo_pgsql
+--FILE--
+<?php
+
+try {
+    new Pdo\Pgsql('pgsql:host=/nonexistent', options: [
+        PDO::ATTR_PERSISTENT => true,
+    ]);
+} catch (Throwable $e) {
+    echo $e::class, ': ', $e->getMessage(), PHP_EOL;
+}
+
+echo "Failed connection object destroyed without crash\n";
+
+?>
+--EXPECTF--
+PDOException: SQLSTATE[08006] [7] %a
+Failed connection object destroyed without crash