fs/iso9660: Prevent read past the end of system use area

fs/iso9660: Prevent read past the end of system use area

In the code, the for loop advanced the entry pointer to the next entry before
checking if the next entry is within the system use area boundary. Another
issue in the code was that there is no check for the size of system use area.
For a corrupted system, the size of system use area can be less than the size
of minimum SUSP entry size (4 bytes). These can cause buffer overrun. The fixes
added the checks to ensure the read is valid and within the boundary.

Signed-off-by: Lidong Chen <lidong.chen@oracle.com>
Reviewed-by: Thomas Schmitt <scdbackup@gmx.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>