fs/iso9660: Prevent skipping CE or ST at start of continuation area

fs/iso9660: Prevent skipping CE or ST at start of continuation area

If processing of a SUSP CE entry leads to a continuation area which
begins by entry CE or ST, then these entries were skipped without
interpretation. In case of CE this would lead to premature end of
processing the SUSP entries of the file. In case of ST this could
cause following non-SUSP bytes to be interpreted as SUSP entries.

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