client-stream metrics don't invoked Handled on OK status

[jgraettinger]

See: https://github.com/grpc-ecosystem/go-grpc-prometheus/blob/master/client_metrics.go#L230-L244

The problem with this block is that CloseAndRecv of a client-only stream sends stream close, receives the single response message, and then never reads stream EOF which would cause Handle to be invoked.

[jgraettinger]

FWIW, a work-around is to add an extra RecvMsg, for purposes of draining the EOF & causing the interceptor to run.