fs/iso9660: Delay CE hop until end of current SUSP area

fs/iso9660: Delay CE hop until end of current SUSP area

The SUSP specs demand that the reading of the next SUSP area which is
depicted by a CE entry shall be delayed until reading of the current
SUSP area is completed. Up to now GRUB immediately ends reading of the
current area and loads the new one. So, buffer the parameters of a found
CE entry and perform checks and reading of new data only after the
reader loop has ended.

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