veyron/runtimes/google/ipc/stream/proxy: Fix race.

Change-Id: I33a054ca2a6e93b6cded60f41edb300ca8e40df1
diff --git a/runtimes/google/ipc/stream/proxy/proxy.go b/runtimes/google/ipc/stream/proxy/proxy.go
index bab175e..e0022d5 100644
--- a/runtimes/google/ipc/stream/proxy/proxy.go
+++ b/runtimes/google/ipc/stream/proxy/proxy.go
@@ -401,7 +401,7 @@
 	// flow). This optimization is left an as excercise to the interested.
 	for cid, bytes := range counters {
 		srcVCI := cid.VCI()
-		if vc := process.servers[srcVCI]; vc != nil {
+		if vc := process.ServerVC(srcVCI); vc != nil {
 			vc.ReleaseCounters(cid.Flow(), bytes)
 			continue
 		}