btrfs: fix invalid inode pointer dereferences during log replay

In a few places where we call read_one_inode(), if we get a NULL pointer
we end up jumping into an error path, or fallthrough in case of
__add_inode_ref(), where we then do something like this:

   iput(&inode->vfs_inode);

which results in an invalid inode pointer that triggers an invalid memory
access, resulting in a crash.

Fix this by making sure we don't do such dereferences.

Fixes: b4c50cbb ("btrfs: return a btrfs_inode from read_one_inode()")
CC: stable@vger.kernel.org # 6.15+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>