Icon library: fill is added to stroke only icons

### How to reproduce

Configure the icon library with icons that are stroke only. `fill` is set to `none` on svg level in each icon asset.

### Expected

Icons show up in the icon library as they are with only stroke but no fill.

### Actual result

Icons show up with `fill` set to `currentcolor` in the icon library.

Start by tracing the icon library's rendering path and how SVG asset attributes are applied when stroke-only icons are configured. Reproduce the issue with an asset whose SVG-level fill is none, then verify that the library preserves no fill and displays only the icon's stroke.

Written by the indexing model from the issue text.