Fix failed query blocking

[hczhu-db]

Shouldn't call parseRequestQueryString() before processing the query.

Tested on a dev region

$ k-m3 dev-azure-westus port-forward query-frontend-read-regional-deployment-7fc87cd49d-2wc95 7201

$ curl 'http://localhost:7201/api/v1/query' -X POST -F 'query=count(up)'
{"status":"success","data":{"resultType":"vector","result":[{"metric":{},"value":[1723075712.91,"2708"]}]}}

[jnyi]

LGTM, thanks for the quick fix