Exit early if SMTP connection fails.

If the SMTP connection is disconnected (read() returns false) we should
exit early and not wait for the read timeout. This has the added benefit
of making the mocks much simpler.

Refs #10221

lib/Cake/Network/Email/SmtpTransport.php

@@ -352,7 +352,11 @@ protected function _smtpSend($data, $checkCode = '250') {
 			$response = '';
 			$startTime = time();
 			while (substr($response, -2) !== "\r\n" && ((time() - $startTime) < $this->_config['timeout'])) {
-				$response .= $this->_socket->read();
+				$bytes = $this->_socket->read();
+				if ($bytes === false || $bytes === null) {
+					break;
+				}
+				$response .= $bytes;
 			}
 			if (substr($response, -2) !== "\r\n") {
 				throw new SocketException(__d('cake_dev', 'SMTP timeout.'));