No icon size error on startup

[KiwiHawk]

Mod list:

• Angel's Refining
• Longhaul Trains

[KiwiHawk]

icon_size :: SpriteSizeType optional The size of the square icon, in pixels. E.g. 32 for a 32px by 32px icon.

Mandatory if icon_size is not specified outside of icons. https://lua-api.factorio.com/latest/types/IconData.html

Need to pass a default size to util.combine_icons https://github.com/wube/factorio-data/blob/70be70ec84485a755e76cd22a3675a88a9106ce5/core/lualib/util.lua#L334