Return REWARD_SHARE_UNKNOWN when trying to cancel non-existent reward-share

src/main/java/org/qortal/transaction/RewardShareTransaction.java

@@ -136,7 +136,7 @@ public class RewardShareTransaction extends Transaction {
 
 			// Deleting a non-existent reward-share makes no sense
 			if (isCancellingSharePercent)
-				return ValidationResult.INVALID_REWARD_SHARE_PERCENT;
+				return ValidationResult.REWARD_SHARE_UNKNOWN;
 
 			// Check the minting account hasn't reach maximum number of reward-shares
 			int rewardShareCount = this.repository.getAccountRepository().countRewardShares(creator.getPublicKey());

src/main/java/org/qortal/transaction/Transaction.java

@@ -225,6 +225,7 @@ public abstract class Transaction {
 		AT_IS_FINISHED(71),
 		NO_FLAG_PERMISSION(72),
 		NOT_MINTING_ACCOUNT(73),
+		REWARD_SHARE_UNKNOWN(76),
 		INVALID_REWARD_SHARE_PERCENT(77),
 		PUBLIC_KEY_UNKNOWN(78),
 		INVALID_PUBLIC_KEY(79),