Fix registrar errors early in the chain

miner/src/service_transaction_checker.rs

@@ -44,12 +44,12 @@ impl ServiceTransactionChecker {
 		client: &C,
 		tx: &SignedTransaction
 	) -> Result<bool, String> {
-		let sender = tx.sender();
 		// Skip checking the contract if the transaction does not have zero gas price
 		if !tx.gas_price.is_zero() {
 			return Ok(false)
 		}
 
+		let sender = tx.sender();
 		self.check_address(client, sender)
 	}
 

util/registrar/src/registrar.rs

@@ -42,9 +42,10 @@ pub trait RegistrarClient: CallContract + Send + Sync {
 		let id = encode_input(hashed_key, DNS_A_RECORD);
 
 		let address_bytes = self.call_contract(block, registrar_address, id)?;
-
+		if address_bytes.is_empty() {
+			return Ok(None)
+		}
 		let address = decode_output(&address_bytes).map_err(|e| e.to_string())?;
-
 		if address.is_zero() {
 			Ok(None)
 		} else {