libext2fs: only link an inode into a directory once

libext2fs: only link an inode into a directory once

The ext2fs_link helper function link_proc does not check the value of
ls->done, which means that if the function finds multiple empty spaces
that will fit the new directory entry, it will create a directory
entry in each of the spaces.  Instead of doing that, check the done
value and don't do anything more if we've already added the directory
entry.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>