Clear dummy substitution after deleting substitution with oldId

aleksis/apps/chronos/frontend/components/substitutions/SubstitutionCard.vue

@@ -250,6 +250,13 @@ export default {
           if (cached[index].oldId) {
             cached[index].id = cached[index].oldId;
             cached[index].oldId = null;
+
+            // Clear dummy substitution
+            cached[index].teachers = [];
+            cached[index].rooms = [];
+            cached[index].subject = null;
+            cached[index].comment = "";
+            cached[index].cancelled = false;
           } else {
             this.$emit("delete", cached[index].datetimeStart);
           }