Fix the coursebook-print-dialog-validation

aleksis/apps/alsijil/frontend/components/coursebook/CoursebookPrintDialog.vue

@@ -129,7 +129,7 @@ export default {
     },
     valid() {
       return (
-        this.currentGroupSelection.length > 0 &&
+        this.selectedGroups.length > 0 &&
         (this.includeMembersTable ||
           this.includeTeachersAndSubjectsTable ||
           this.includePersonOverviews ||