btrfs: fix iteration of extrefs during log replay

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

btrfs: fix iteration of extrefs during log replay

At __inode_add_ref() when processing extrefs, if we jump into the next

label we have an undefined value of victim_name.len, since we haven't

initialized it before we did the goto. This results in an invalid memory

access in the next iteration of the loop since victim_name.len was not

initialized to the length of the name of the current extref.

Fix this by initializing victim_name.len with the current extref's name

length.