The shash ahash digest adaptor function may crash if given a
zero-length input together with a null SG list. This is because
it tries to read the SG list before looking at the length.
This patch fixes it by checking the length first.
Cc: <[email protected]>
Reported-by: Stephan Müller<[email protected]>
Signed-off-by: Herbert Xu <[email protected]>
Tested-by: Stephan Müller <[email protected]>