Fix new phpstan errors

Author: alecpl

program/lib/Roundcube/rcube.php

@@ -1408,7 +1408,7 @@ public static function raise_error($arg, $log = false, $terminate = false)
                 'file' => $arg->getFile(),
                 'message' => $arg->getMessage(),
             ];
-        } elseif (is_object($arg) && is_a($arg, 'PEAR_Error')) {
+        } elseif ($arg instanceof PEAR_Error) {
             $info = $arg->getUserInfo();
             $arg = [
                 'code' => $arg->getCode(),

program/lib/Roundcube/rcube_smtp.php

@@ -247,11 +247,6 @@ public function send_mail($from, $recipients, $headers, $body, $opts = [])
 
         // prepare list of recipients
         $recipients = $this->_parse_rfc822($recipients);
-        if (is_a($recipients, 'PEAR_Error')) {
-            $this->error = ['label' => 'smtprecipientserror'];
-            $this->reset();
-            return false;
-        }
 
         $exts = $this->conn->getServiceExtensions();
         $from_params = null;