correction for mandatory fields in forms

Signed-off-by: Michael Kaufmann <d00p@froxlor.org>

lib/formfields/customer/email/formfield.emails_edit.php

@@ -118,6 +118,11 @@ return [
 					]
 				]
 			]
+		],
+		'buttons' => [
+			[
+				'label' => lng('panel.backtooverview')
+			]
 		]
 	]
 ];