libext2fs: directory iteration mustn't walk off the buffer end

libext2fs: directory iteration mustn't walk off the buffer end

When we're iterating a directory, the loop control code reads the
length of the next directory record, failing to account for the fact
that there must be at least 8 bytes (the minimum size of a directory
entry) left in the buffer to read the next directory record.  Fix the
loop conditional so that we don't read off the end of the buffer.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reported-by: Sami Liedes <sami.liedes@iki.fi>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>