[lazy-mode] this.$fireModule returns null IF this.$fire...Ready() is called in the same component

### Version
@nuxtjs/firebase: 
firebase: 
nuxt: 

### Steps to reproduce
setup firebase as you normally do in nuxtjs
then call await this.$fire.firestoreReady()
then console.log(this.$fireModule)

### What is actually happening?
the output is undifined