runtime: fix multi chan recv/send select

cl/_testgo/selects/in.go

@@ -0,0 +1,30 @@
+package main
+
+func main() {
+	c1 := make(chan struct{}, 1)
+	c2 := make(chan struct{}, 1)
+	c3 := make(chan struct{}, 1)
+	c4 := make(chan struct{}, 1)
+
+	go func() {
+		<-c1
+		println("<-c1")
+
+		select {
+		case c2 <- struct{}{}:
+			println("c2<-")
+		case <-c3:
+			println("<-c3")
+		}
+	}()
+
+	c1 <- struct{}{}
+	println("c1<-")
+
+	select {
+	case <-c2:
+		println("<-c2")
+	case <-c4:
+		println("<-c4")
+	}
+}