runtime: handle negative sleep times

This change fixes the edge case where a negative sleep time is provided.
When this happens, the call now returns immediately (as specified by the docs for time.Sleep).

src/runtime/scheduler_any.go

@@ -1,3 +1,4 @@
+//go:build !scheduler.none
 // +build !scheduler.none
 
 package runtime
@@ -7,6 +8,10 @@ import "internal/task"
 // Pause the current task for a given time.
 //go:linkname sleep time.Sleep
 func sleep(duration int64) {
+	if duration <= 0 {
+		return
+	}
+
 	addSleepTask(task.Current(), nanosecondsToTicks(duration))
 	task.Pause()
 }

src/runtime/scheduler_none.go

@@ -1,9 +1,14 @@
+//go:build scheduler.none
 // +build scheduler.none
 
 package runtime
 
 //go:linkname sleep time.Sleep
 func sleep(duration int64) {
+	if duration <= 0 {
+		return
+	}
+
 	sleepTicks(nanosecondsToTicks(duration))
 }