pdbcycle: removed extra iteration of read locations
pdbcycle: removed extra iteration of read locations

summary: when we read locations during Read() call, we had two loops.
One was incrementing stats information and other was updating return
value. Both the iterations was on same data slice. If we look at system
as a whole there are multiple go-routines calling this Read api for
multiple datum's. Having one iteration should speed some cpu time by a
small factor.

test: ran all unit test cases

signalfx/golib,signalfx/golib