ext4: fix potential use after free in __ext4_journal_stop

ext4: fix potential use after free in __ext4_journal_stop

There is a use-after-free possibility in __ext4_journal_stop() in the
case that we free the handle in the first jbd2_journal_stop() because
we're referencing handle->h_err afterwards. This was introduced in
8426e137a165805af1655310a36559c58c0649e3 and it is wrong. Fix it by
storing the handle->h_err value beforehand and avoid referencing
potentially freed handle.

Fixes: 8426e137a165805af1655310a36559c58c0649e3
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Cc: stable@vger.kernel.org