Merge pull request #1923 from guggero/base58-fix

base58: fix decoding issue

btcutil/base58/base58.go

@@ -55,6 +55,10 @@ func Decode(b string) []byte {
 
 		total := uint64(0)
 		for _, v := range t[:n] {
+			if v > 255 {
+				return []byte("")
+			}
+
 			tmp := b58[v]
 			if tmp == 255 {
 				return []byte("")

btcutil/base58/base58_test.go

@@ -43,6 +43,8 @@ var invalidStringTests = []struct {
 	{"4kl8", ""},
 	{"0OIl", ""},
 	{"!@#$%^&*()-_=+~`", ""},
+	{"abcd\xd80", ""},
+	{"abcd\U000020BF", ""},
 }
 
 var hexTests = []struct {