construct the datasource for the example query if not added (#57936)

public/app/features/query/components/QueryEditorRow.tsx

@@ -318,6 +318,10 @@ export class QueryEditorRow<TQuery extends DataQuery> extends PureComponent<Prop
   };
 
   onClickExample = (query: TQuery) => {
+    if (query.datasource === undefined) {
+      query.datasource = { type: this.props.dataSource.type, uid: this.props.dataSource.uid };
+    }
+
     this.props.onChange({
       ...query,
       refId: this.props.query.refId,