jfs: array-index-out-of-bounds fix in dtReadFirst

[ Upstream commit ca84a2c9be482836b86d780244f0357e5a778c46 ]

The value of stbl can be sometimes out of bounds due
to a bad filesystem. Added a check with appopriate return
of error code in that case.

Reported-by:  <syzbot+65fa06e29859e41a83f3@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=65fa06e29859e41a83f3


Signed-off-by: Ghanshyam Agrawal <ghanshyam1898@gmail.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>