Fix deprecated warning in ADODB_postgres64::qStr()

pg_escape_string() will trigger a deprecation warning in PHP 8.1+ when
there is no connection specified. This can occur when using
setSessionVariables() in the load balancer, so we fall back to emulated
escaping in this case.

Fixes #956

drivers/adodb-postgres64.inc.php

@@ -258,7 +258,9 @@ function qStr($s, $magic_quotes=false)
 		if ($this->_connectionID) {
 			return "'" . pg_escape_string($this->_connectionID, $s) . "'";
 		} else {
-			return "'" . pg_escape_string($s) . "'";
+			// Fall back to emulated escaping when there is no database connection.
+			// Avoids errors when using setSessionVariables() in the load balancer.
+			return parent::qStr( $s );
 		}
 	}