Fix activation of periods

Did not make a difference. But now it's proper anyhow.

aleksis/apps/alsijil/frontend/components/coursebook/absences/AbsenceCreationForm.vue

@@ -112,9 +112,9 @@ export default {
     allPersons: persons,
     periodsByDay: {
       query: periodsByDay,
-        this.handleStartDate(this.start);
-        this.handleEndDate(this.end);
       result(_) {
+        this.handleStartDate(this.start.toISO());
+        this.handleEndDate(this.end.toISO());
       },
     },
   },