Fix Panic in TestServer_ConcurrentPointsWriter_Subscribe
Fix Panic in TestServer_ConcurrentPointsWriter_Subscribe

If the server is closed an write is sent, the LocalServer panics.

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