Fall back to default resourcepack icon if missing pack.png

[saadndm]

The OSL resource loader should fall back to MC's default resource pack icon instead of TextureUtil.MISSING_TEXTURE in ResourcePackSummaryEntry.java.

Rn a pack without pack.png gets the missing texture:

        try (InputStream is = summary.open().getResource(ResourcePack.ICON_FILE)) {
            icon = new DynamicTexture(TextureUtil.readImage(is));
        } catch (Throwable t) {
            icon = TextureUtil.MISSING_TEXTURE;
        }

In vanilla, if pack.png is missing, it falls back to the default resource pack icon