Add support for save buttons in scheduler task edit screen

[Former user]

If EXT:unroll is active the save buttons in the screen to add or edit a scheduler task are removed. If the option "basic.unroll" is deactivated creating or editing a scheduler task ends in a fatal error:

Call to a member function getClasses() on null in D:[...]\vendor\typo3\cms\typo3\sysext\backend\Classes\Template\Components\Buttons\SplitButton.php on line 141

The extension needs to be deactivated completely in order to allow scheduler tasks to be saved.

Regards, Jigal van Hemert <jigal.van.hemert [at] typo3.org>