libblkid: prevent OOB access while probing HFS+

libblkid: prevent OOB access while probing HFS+

It is possible to perform out of boundary read accesses due to
insufficient boundary checks in probe_hfsplus.

The first issue occurs if the leaf count in a B-node is too
small. The second happens while parsing a unicode description which
is longer than 255 UTF-8 characters. The length is stored in a 16 bit
integer, but the array in the struct is limited to 255 * 2, which is
in sync with Apple's Open Source HFS+ implementation (HFSUniStr255).

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>