resize2fs: fix ENOSPC corruption case

resize2fs: fix ENOSPC corruption case

http://people.redhat.com/esandeen/livecd-creator-imagefile.bz2
contains an image (for now) which, when resized to 578639, corrupts
the filesystem.

This is a bit crazy, I guess, because the fs currently has only
1 free block, but still, we should be graceful about the failure.
Perhaps it would make sense to check the requested valuea against
the minimum value resize2fs would compute for "-P" and fail (at
least without a force).

But in any case, this exposed 2 bugs when moving that one block
required an extent split, which is what hit the ENOSPC.

For starters, ext2fs_extent_set_bmap() in the "(re/un)mapping last
block in extent" case was replacing the old extent before the
new one was created; when the new extent creation failed, it
left us in an inconsistent state.  Simply changing the order of
the two should fix this problem.

Next, ext2fs_extent_insert was calling ext2fs_extent_delete()
on *any* error, including one caused by failure to allocate a new
block to split the node to hold that extent ... the handle was left
unchanged, and we deleted the -original- extent.

As a quick fix for this, just don't do the delete if we fail the split,
though this may need to be smarter.  I don't think we have terribly
consistent behavior about where a handle is left on various errors.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>