examples: Use "or" operator in transfer check of NEP5 token

CanTransfer function checks if "to" and "from" values are
correct script hashes. If one of these values is correct and one
incorrect, then function returns false positive result. It uses "and"
operator which requires both "to" and "from" script hashes to be
incorrect to fail transaction.

Instead transaction must fail if at least one argument is incorrect,
so it should be "or" operator.

examples/token/nep5/nep5.go

@@ -58,7 +58,7 @@ func (t Token) Transfer(ctx storage.Context, from []byte, to []byte, amount int)
 
 // CanTransfer returns the amount it can transfer
 func (t Token) CanTransfer(ctx storage.Context, from []byte, to []byte, amount int) int {
-	if len(to) != 20 && !IsUsableAddress(from) {
+	if len(to) != 20 || !IsUsableAddress(from) {
 		return -1
 	}