Prevent auth bypass with PostgreSQL connections

Thanks to Emmet Leahy of Sorcery Ltd for reporting this vulnerability
(CVE-2021-3850).

This is a minimalistic approach to patch the issue, to reduce the risk
of causing regressions in the legacy stable branch.

Fixes #793

drivers/adodb-postgres64.inc.php

@@ -51,7 +51,6 @@ function adodb_addslashes($s)
 {
 	$len = strlen($s);
 	if ($len == 0) return "''";
-	if (strncmp($s,"'",1) === 0 && substr($s,$len-1) == "'") return $s; // already quoted
 
 	return "'".addslashes($s)."'";
 }