Bad error message for loading empty string as an asset.

## What problem does this solve or what need does it fill?

This is the error message, "" is not printed and asset type is missing, making it completely unusable for debugging purpose.

```
Encountered an I/O error while loading asset: Is a directory (os error 21)
```

## What solution would you like?

Change this somehow.

Start by reproducing the empty-string asset load that produces the shown I/O error, then trace the asset-loading error path. Done means the resulting error identifies the empty input and includes the asset type so the failure is useful for debugging.

Written by the indexing model from the issue text.