ext4: xattr: fix null pointer deref in ext4_raw_inode()

In the Linux kernel, the following vulnerability has been resolved: ext4: xattr: fix null pointer deref in ext4_raw_inode() If ext4_get_inode_loc() fails (e.g. if it returns -EFSCORRUPTED), iloc.bh will remain set to NULL. Since ext4_xattr_inode_dec_ref_all() lacks error checking, this will lead to a null pointer dereference in ext4_raw_inode(), called right after ext4_get_inode_loc(). Found by Linux Verification Center (linuxtesting.org) with SVACE.