Resolve "Creating absence fails / absence reasons do not load"

Closes #311 (closed)

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

@@ -67,7 +67,7 @@
         v-if="form"
         @click="form = false"
         :loading="loading"
-        :disabled="!formValid"
+        :disabled="!formValid || !absenceReason"
       >
         {{ $t("actions.continue") }}
         <v-icon right>$next</v-icon>