ext4: check if in-inode xattr is corrupted in ext4_expand_extra_isize_ea()

We aren't checking to see if the in-inode extended attribute is
corrupted before we try to expand the inode's extra isize fields.

This can lead to potential crashes caused by the BUG_ON() check in
ext4_xattr_shift_entries().

Upstream commit: 9e92f48c34eb2b9af9d12f892e2fe1fce5e8ce35
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Change-Id: Ia66e005d04bf9eccb7febd8cb0733a67f9a4faf4
Git-commit: 1f002539e6da1e03cede84fb3416c58dae2f6f66
Git-repo: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git


Signed-off-by: Andrey Markovytch <andreym@codeaurora.org>