avoid pushing the same ref more than once (fix #4253)
avoid pushing the same ref more than once (fix #4253)

Kingwl/vue,vuejs/vue,leemotive/vue,KingMario/vue,hanhongyuan/vue,xueyaodeai/vue,greennyreborn/vue,vuejs/vue,KingMario/vue,Jinjiang/vue,KingMario/vue,cnchanning/vue,Kingwl/vue,greennyreborn/vue,lizhiyao/vue,vuejs/vue,lizhiyao/vue,leemotive/vue,xueyaodeai/vue,Jinjiang/vue,xueyaodeai/vue,Hanks10100/vue,cnchanning/vue,leemotive/vue,vuejs/vue,hanhongyuan/vue,lizhiyao/vue,cnchanning/vue,Jinjiang/vue,hanhongyuan/vue,Kingwl/vue,Ddder-FE/vue,KingMario/vue,Ddder-FE/vue,greennyreborn/vue,optimizely/vue,lizhiyao/vue,Hanks10100/vue,greennyreborn/vue,Hanks10100/vue,hanhongyuan/vue,Ddder-FE/vue,Kingwl/vue,xueyaodeai/vue,Jinjiang/vue,Ddder-FE/vue,leemotive/vue,Hanks10100/vue