libext2fs: display partial path if fs corrupted in ext2fs_get_pathname()

libext2fs: display partial path if fs corrupted in ext2fs_get_pathname()

The function ext2fs_get_pathname() used to return EXT2_ET_NO_DIRECTORY
if one of the directories in an inode's pathname is not a directory.
This is not very useful in an emergency, when the file system is
corrupted.  This commit will cause ext2fs_get_pathname() to return a
partial pathname, which should help system administrators trying to
use debugfs to investigate a corrupted file system.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>