Loki: Use queries `maxLines` if configured, even if it is zero (#61652)

* user `query.maxLines` even if it is zero

* remove unnecessary comment

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

@@ -176,6 +176,10 @@ describe('LokiDatasource', () => {
       await runTest(80, '40', 80, undefined);
     });
 
+    it('should use query max lines, if both exist, even if it is 0', async () => {
+      await runTest(0, '40', 0, undefined);
+    });
+
     it('should report query interaction', async () => {
       await runTest(80, '40', 80, CoreApp.Explore);
       expect(reportInteraction).toHaveBeenCalledWith(

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

@@ -174,7 +174,7 @@ export class LokiDatasource
   query(request: DataQueryRequest<LokiQuery>): Observable<DataQueryResponse> {
     const queries = request.targets
       .map(getNormalizedLokiQuery) // "fix" the `.queryType` prop
-      .map((q) => ({ ...q, maxLines: q.maxLines || this.maxLines })); // set maxLines if not set
+      .map((q) => ({ ...q, maxLines: q.maxLines ?? this.maxLines }));
 
     const fixedRequest: DataQueryRequest<LokiQuery> & { targets: LokiQuery[] } = {
       ...request,