NbLayoutHeaderComponent set fixed=false also if subheader=false

[matzrm]

Issue type

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• [ X ] bug report
• [ ] feature request

Issue description

Fixed is setted to false also if subheader=false

Current behavior:

set nb-layout-header in this way: <nb-layout-header [fixed]="true" [subheader]="false">

Expected behavior:

NbLayoutHeaderComponent have to check subheader value before set to false fixed. Steps to reproduce:

Checkout ngx-admin and then add to @theme/layouts/components/one-column.layout.html <nb-layout-header [fixed]="true" [subheader]="false"> Related code:

insert short code snippets here

Other information:

npm, node, OS, Browser

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Angular, Nebular

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