Fix a logic error in ASN1_item_sign_ctx()

Fix a logic error in ASN1_item_sign_ctx()

If the item_sign() ASN.1 method returns 1, it supposedly handles everything
and the goto err prior to r1.5 was actually a success path. Go figure.

This is fortunately inconsequential since there are only two item_sign()
methods, one for RSA and one for Ed25519, neither of which can return 1.
They only return 0, 2, and 3.

Pointed out by and ok jsing