fix: set the correct asset_info when extracting css

[inottn]

Summary

fix #8431

The default asset_info is returned here:

rspack/crates/rspack_plugin_extract_css/src/plugin.rs

Line 415 in 9112e35

AssetInfo::default(),

Therefore, the contenthash cannot be obtained here, leading to an unexpected termination of the subsequent process:

rspack/crates/rspack_plugin_real_content_hash/src/lib.rs

Lines 73 to 75 in 9112e35

	if hash_to_asset_names.is_empty() {
	return Ok(());
	}

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[JSerFeng]

Thanks !