Explore/Loki: Fix handling of legacy log row context request (#21767)

Closes #21695

public/app/plugins/datasource/loki/datasource.ts

@@ -491,6 +491,7 @@ export class LokiDatasource extends DataSourceApi<LokiQuery, LokiOptions> {
         switchMap((res: { data: LokiStreamResponse; status: number }) =>
           iif(
             () => res.status === 404,
+            defer(() =>
               this._request(LEGACY_QUERY_ENDPOINT, target).pipe(
                 catchError((err: any) => {
                   const error: DataQueryError = {
@@ -503,13 +504,16 @@ export class LokiDatasource extends DataSourceApi<LokiQuery, LokiOptions> {
                 map((res: { data: LokiLegacyStreamResponse }) => ({
                   data: res.data ? res.data.streams.map(stream => legacyLogStreamToDataFrame(stream, reverse)) : [],
                 }))
+              )
             ),
+            defer(() =>
               of({
                 data: res.data ? res.data.data.result.map(stream => lokiStreamResultToDataFrame(stream, reverse)) : [],
               })
             )
           )
         )
+      )
       .toPromise();
   };