MINOR: stream: don't update s->lat_time when the wakeup date is not set

In 2.7 was added a stream wakeup latency calculation with commit
6a28a30 ("MINOR: tasks: do not keep cpu and latency times in struct
task"). However, due to the transformation of the previous code, it
kept unconditionally updating s->lat_time even of the sched_wake_date
was zero. In other words, s->lat_time is constantly updated for the
huge majority of calls that are made without profiling. Let's just
check the sched_wake_date status before doing so.

Author: wtarreau

src/stream.c

@@ -1639,8 +1639,12 @@ static void stream_handle_timeouts(struct stream *s)
  */
 static void stream_cond_update_cpu_latency(struct stream *s)
 {
-	uint32_t lat = th_ctx->sched_call_date - th_ctx->sched_wake_date;
+	uint32_t lat;
 
+	if (likely(!th_ctx->sched_wake_date))
+		return;
+
+	lat = th_ctx->sched_call_date - th_ctx->sched_wake_date;
 	s->lat_time += lat;
 }