nb-layout-header is not getting rendered if placed into separate component

### Issue type

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

* [x ] bug report
* [ ] feature request

### Issue description

**Current behavior:**

`nb-layout-header` is not getting rendered if I place this into another component
**Expected behavior:**

Header should be rendered
**Steps to reproduce:**

- Created new app

- Create another module

- Created homepage component with following code
```

Company Name

Card





```
This works as expected and I get header.

- Create another component named as `header` and place following code into that
```
Company Name
```

- Now add this `header` component into parent component, like
```

Card





```
No header comes on the browser this time.

### Other information:

**npm, node, OS, Browser**
```
npm version : 6.11.3
node version 10.16.0
Angular CLI 8.3.5
Nebular Theme 4.3.1
```

**Angular, Nebular**
```

```
[StackBlitz Link](https://stackblitz.com/github//ShahnazK/nebtest)