Bug 2378978 (CVE-2025-38243)

In the Linux kernel, the following vulnerability has been resolved:

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.