all: fix issues reported by honnef.co/go/simple/cmd/gosimple

crypto/crypto_test.go

@@ -217,7 +217,7 @@ func TestValidateSignatureValues(t *testing.T) {
 
 func checkhash(t *testing.T, name string, f func([]byte) []byte, msg, exp []byte) {
 	sum := f(msg)
-	if bytes.Compare(exp, sum) != 0 {
+	if !bytes.Equal(exp, sum) {
 		t.Fatalf("hash %s mismatch: want: %x have: %x", name, exp, sum)
 	}
 }

crypto/ecies/ecies.go

@@ -291,9 +291,8 @@ func Encrypt(rand io.Reader, pub *PublicKey, m, s1, s2 []byte) (ct []byte, err e
 
 // Decrypt decrypts an ECIES ciphertext.
 func (prv *PrivateKey) Decrypt(rand io.Reader, c, s1, s2 []byte) (m []byte, err error) {
-	if c == nil || len(c) == 0 {
-		err = ErrInvalidMessage
-		return
+	if len(c) == 0 {
+		return nil, ErrInvalidMessage
 	}
 	params := prv.PublicKey.Params
 	if params == nil {