Customizing menu renderIcon feature

[zce]

The renderIcon function of the custom menu cannot control whether icons are used.

This function solves the problem (这个功能解决的问题)

Consider not enabling icons when a function returns null or false.

Expected API (期望的 API)

const renderMenuIcon = option => {
  if (!option.icon) return null
  return h(NIcon, null, { default: option.icon })
}