knownhosts: fix hashed hostname component count in error message

Correct the component splitting in the nextWord function to omit the
initial empty element when decoding the pipe-separated hostname hash.

Previously, the error message incorrectly counted this empty element,
leading to misleading errors like:

  knownhosts: got 3 components, want 3

This change makes the component split start from index 1.

The existing tests cover the changed code.

Signed-off-by: Kimmo Lehto <klehto@mirantis.com>

Author: kke

ssh/knownhosts/knownhosts.go

@@ -481,17 +481,17 @@ func decodeHash(encoded string) (hashType string, salt, hash []byte, err error)
 		err = errors.New("knownhosts: hashed host must start with '|'")
 		return
 	}
-	components := strings.Split(encoded, "|")
-	if len(components) != 4 {
+	components := strings.Split(encoded[1:], "|")
+	if len(components) != 3 {
 		err = fmt.Errorf("knownhosts: got %d components, want 3", len(components))
 		return
 	}
 
-	hashType = components[1]
-	if salt, err = base64.StdEncoding.DecodeString(components[2]); err != nil {
+	hashType = components[0]
+	if salt, err = base64.StdEncoding.DecodeString(components[1]); err != nil {
 		return
 	}
-	if hash, err = base64.StdEncoding.DecodeString(components[3]); err != nil {
+	if hash, err = base64.StdEncoding.DecodeString(components[2]); err != nil {
 		return
 	}
 	return