Fix ForeignKeyField not returning object when attribute is set and new object is created

aleksis/core/frontend/components/generic/forms/ForeignKeyField.vue

@@ -109,7 +109,7 @@ export default {
     handleSave(data) {
       let newItem =
         data.data[this.gqlCreateMutation.definitions[0].name.value].item;
-      let newValue = this.$attrs["return-object"] ? newItem : newItem.id;
+      let newValue = "return-object" in this.$attrs ? newItem : newItem.id;
       let modelValue =
         "multiple" in this.$attrs
           ? Array.isArray(this.$attrs.value)