Account for empty path strings in VFS

Title.

Some of our current VFS tests allow for performing read/write operations on empty file path strings. We should not allow this. Fix the VFS implementation to return errors when being asked to perform file IO on an empty path string.

Locate the VFS implementation and the tests that currently allow read/write operations on empty path strings. Run the relevant VFS tests first; done means file I/O requests with an empty path return errors while valid paths continue to work.

Written by the indexing model from the issue text.