crypto: algif_hash - Remove bogus SGL free on zero-length error path

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

crypto: algif_hash - Remove bogus SGL free on zero-length error path

When a zero-length message is hashed by algif_hash, and an error is triggered, it tries to free an SG list that was never allocated in the first place. Fix this by not freeing the SG list on the zero-length error path.