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)