backend: add close status chan for backend

Fix #I1TOQY

reason: 
1. add close status chan for backend
2. use closeStatusChan instead of directly closing
Signed-off-by: Nyangfeiyu <yangfeiyu2@huawei.com>

daemon/build.go

@@ -60,7 +60,7 @@ func (b *Backend) Build(req *pb.BuildRequest, stream pb.Control_BuildServer) err
 	eg, ctx := errgroup.WithContext(ctx)
 	eg.Go(func() error {
 		b.syncBuildStatus(req.BuildID) <- struct{}{}
-		close(b.status[req.BuildID].startBuild)
+		b.closeStatusChan(req.BuildID)
 		var berr error
 		imageID, berr = builder.Build()
 

daemon/status.go

@@ -63,3 +63,11 @@ func (b *Backend) syncBuildStatus(buildID string) chan struct{} {
 	b.Unlock()
 	return statusChan
 }
+
+func (b *Backend) closeStatusChan(buildID string) {
+	b.Lock()
+	if _, ok := b.status[buildID]; ok {
+		close(b.status[buildID].startBuild)
+	}
+	b.Unlock()
+}