Incorrect theme

### Issue type

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

* [x] bug report
* [ ] feature request
* [ ] question about the decisions made in the repository

### Issue description

**Current behavior:**

I've set a localStorage and tried to set the name of theme in `theme.modules.ts`:

```
...

const NB_THEME_PROVIDERS = [
...NbThemeModule.forRoot(
{
name: ((localStorage.getItem('theme') === 'corporate' || localStorage.getItem('theme') === 'default') ? localStorage.getItem('theme') : 'cosmic')
},
...
];

...
```
But no one theme is load (not even the 'cosmic' theme).
In that issue, I insert 2 prints showing how the error occurs: https://github.com/akveo/ngx-admin/issues/1980
This happens only on production mode

**Expected behavior:**
Change theme if a localStorage's item has setted (or other way).

### Other information:

**npm, node, OS, Browser**
```
Node, npm: v9.11.1 and 5.6.0
OS: Windows 8.1
Browser: Chrome
```

**Angular, Nebular**
```
Angular: 7.2.3
Nebular: 3.0.0
```