e2fsck: Fix directory with holes even when i_size is wrong

e2fsck: Fix directory with holes even when i_size is wrong

The old method for detecting directories with holes depended on i_size
being correct, even though the correct value of i_size hadn't been
calculated yet.  Hence, a directory inode with holes and an i_size of
0 would require two e2fsck passes to fix completely.

The replacement method for determining whether or not
ext2fs_add_dir_block() should be called is more reliable, and reduces
the size of e2fsck and makes the code more readable as a bonus.

Thanks to Mikulas Patocka for providing a sample file system which
demonstrated this problem.

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