image_delete: move name check first

Signed-off-by: Ma Shimiao <mashimiao.fnst@cn.fujitsu.com>

daemon/image_delete.go

@@ -27,6 +27,10 @@ func (daemon *Daemon) ImageDelete(name string, force, noprune bool) ([]types.Ima
 }
 
 func (daemon *Daemon) imgDeleteHelper(name string, list *[]types.ImageDelete, first, force, noprune bool) error {
+	if name == "" {
+		return fmt.Errorf("Image name can not be blank")
+	}
+
 	var repoName, tag string
 	repoAndTags := make(map[string][]string)
 
@@ -36,10 +40,6 @@ func (daemon *Daemon) imgDeleteHelper(name string, list *[]types.ImageDelete, fi
 		tag = tags.DefaultTag
 	}
 
-	if name == "" {
-		return fmt.Errorf("Image name can not be blank")
-	}
-
 	img, err := daemon.Repositories().LookupImage(name)
 	if err != nil {
 		if r, _ := daemon.Repositories().Get(repoName); r != nil {
@@ -54,7 +54,6 @@ func (daemon *Daemon) imgDeleteHelper(name string, list *[]types.ImageDelete, fi
 	}
 
 	byParents := daemon.Graph().ByParent()
-
 	repos := daemon.Repositories().ByID()[img.ID]
 
 	//If delete by id, see if the id belong only to one repository