fs: ext4: Prevent infinite loop in ext4fs_iterate_dir

fs: ext4: Prevent infinite loop in ext4fs_iterate_dir

If the ext3 journal gets out of sync with what is written on disk, for
example because of an unexpected power cut, ext4fs_read_file can
return an all-zero directory entry.  In that case, ext4fs_iterate_dir
would infinite loop.

This patch detects when a directory entry's direntlen member is 0 and
returns a failure status, which breaks out of the infinite loop.  As a
result, U-Boot will not find files that may subsequently be recovered
when the journal is replayed.

This is better behaviour than hanging in an infinite loop, but as a
further improvement maybe U-Boot could interpret the ext3 journal and
actually find the unsynced entries.

Signed-off-by: Thomas Fitzsimmons <fitzsim@cisco.com>
Reviewed-by: Stefan Roese <sr@denx.de>