Prevent infinite looping while using change method of tab component with angularfire library

### Issue type

**I'm submitting a ...** (check one with "x")

* [x] bug report

### Issue description

**Current behavior:**
I am using Nebular NbTabsetComponent and using (changeTab) event and on every change event I am trying to communicate with the realtime db of firebase using [Angularfire](https://github.com/angular/angularfire) Now when I am using these two in combination, It is constantly tying to hit the database path and infinite loop is forming.

**Expected behavior:**
On change of the tab it should just hit the path only once.

```

onTabClick(tabTitle: string) {
this.loading = true;
// talking to the service to get the data
this.service.serviceMethod()
.pipe(take(1))
.subscribe((data) => {
this.loading = false;
})
}

constructor(private readonly db: AngularFireDatabase) { }

serviceMethod(){
return this.db.list(`/db-path`).valueChanges();
}