Error emerging pinba-engine-9999

I get mysql sources error when emerging pinba-engine:

```
MySQL/MariaDB sources not found at path: /var/tmp/portage//work/_build
```

Looks like `best_version` returns nothing.

```
# emerge -s mariadb
*  dev-db/mariadb
    Latest version available: 10.0.21
    Latest version installed: 10.0.21
```
