Fix leaked goroutine in FileStore.WalkKeys
Fix leaked goroutine in FileStore.WalkKeys

If fn returned and error, the goroutines sending keys from TSM files
would get blocked indefinitely and leak.

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