5.751: `character_gallery` layout prioritizes fitting `ssf2x/gba_portraits` over filling the canvas

[Wolfy76700]

When using the character_gallery layout widget with the ssf2x/gba_portraits assets, using the config below:

{
  "assets": {
    "default": {
    },
    "ssf2x": {
        "asset_key": "gba_portrait",
        "custom_zoom": 1.0
    }
  }
}

and when setting the character_gallery resolution to a tall one (e.g. 200x700), we can see that the layout prioritizes fitting the whole image, instead of trying to fill the canvas, as would be the baseline for a 1.0 zoom value. (See screenshot)