fix #10595: fix panic in Prometheus read API
fix #10595: fix panic in Prometheus read API

nooproblem/influxdb,influxdb/influxdb,mark-rushakoff/influxdb,influxdata/influxdb,influxdb/influxdb,mark-rushakoff/influxdb,influxdb/influxdb,li-ang/influxdb,nooproblem/influxdb,influxdb/influxdb,influxdb/influxdb,nooproblem/influxdb,nooproblem/influxdb,mark-rushakoff/influxdb,mark-rushakoff/influxdb,li-ang/influxdb,nooproblem/influxdb,mark-rushakoff/influxdb,mark-rushakoff/influxdb,influxdb/influxdb,influxdata/influxdb