feat: avoid chdir inside RootDir if disk is not enabled

What does this MR do?

RootDir is only used by zip serving for AllowedPaths when handling the file protocol.

It is not used if disk is not enabled (type file and type zip using file:// returns ErrDiskDisabled).

TODO

• I added the Changelog trailer (e.g. Changelog: added) to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines