Fix 169577: SGN_End crashes if DSA signature fails.
Fix 169577: SGN_End crashes if DSA signature fails.

ekr/nss-old,ekr/nss-old,nmav/nss,ekr/nss-old,nmav/nss,ekr/nss-old,nmav/nss,nmav/nss,ekr/nss-old,ekr/nss-old,nmav/nss,nmav/nss,ekr/nss-old,nmav/nss