Button | loadingIcon is not displayed when icon is not provided

[Urtgard]

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https://stackblitz.com/edit/primeng-button-demo-ysmtsh?file=src%2Fapp%2Fapp.component.html

Current behavior
loadingIcon is not displayed when icon attribute is not provided and button element is used.

Expected behavior
loadingIcon should be displayed even if no icon is set.

Minimal reproduction of the problem with instructions

<button pButton label="Search" [loading]="true"></button>
<button pButton label="Search" icon=" " [loading]="true"></button>
<p-button label="Search" [loading]="true"></p-button>