block: Make path_combine() return the path

block: Make path_combine() return the path

Besides being safe for arbitrary path lengths, after some follow-up
patches all callers will want a freshly allocated buffer anyway.

In the meantime, path_combine_deprecated() is added which has the same
interface as path_combine() had before this patch. All callers to that
function will be converted in follow-up patches.

Signed-off-by: Max Reitz <[email protected]>
Reviewed-by: Alberto Garcia <[email protected]>
Reviewed-by: Kevin Wolf <[email protected]>
Message-id: 20190201192935[email protected]
Signed-off-by: Max Reitz <[email protected]>