[BUG] - uninitialized currentPath in Filesystem can enter folders in file system top

[djdiskmachine]

This part
`
if (currentPath[currentPath.size()-1] != '/')
{
currentPath += "/";
}

return Path(currentPath+leaf);
`

when currentPath is uninitialized will descend into /leaf instead of the intended ./leaf
Piggy shouldn't accidentally give access to folders in the top of the file system.

[djdiskmachine]

Solved in Save As refactor