Minor UI bug in udpbroadcastrelay

[soz]

Just wanted to report a bug on the new udpbroadcastrelay package. If you forget to select interfaces when adding a new instance, you get an error and then the main dashboard also starts showing an error message "Netgate pfSense Plus has detected a crash report or programming bug".

To repro, just click the Add button on the UDP Broadcast Relay page and click Save without entering any information. To work around the bug, just enter all the required information before clicking Save.

Report details:

PHP Errors:
[27-May-2023 10:10:59 US/Pacific] PHP Fatal error:  Uncaught TypeError: implode(): Argument #1 ($pieces) must be of type array, string given in /usr/local/www/udpbroadcastrelay_edit.php:63
Stack trace:
#0 /usr/local/www/udpbroadcastrelay_edit.php(63): implode(',', NULL)
#1 {main}
  thrown in /usr/local/www/udpbroadcastrelay_edit.php on line 63