rpc: getreceivedbylabel, don't loop over the entire wallet txs map if no destinations were found for the input label.

If wallet.GetLabelAddresses() returns an empty vector (the wallet does not have addresses with that label in the addressbook) or if none of the returned destinations are from the wallet, we can return the function right away.

test/functional/wallet_listreceivedby.py

@@ -131,6 +131,9 @@ class ReceivedByTest(BitcoinTestFramework):
         txid = self.nodes[0].sendtoaddress(addr, 0.1)
         self.sync_all()
 
+        # getreceivedbylabel returns an error if the wallet doesn't own the label
+        assert_raises_rpc_error(-4, "Label not found in wallet", self.nodes[0].getreceivedbylabel, "dummy")
+
         # listreceivedbylabel should return received_by_label_json because of 0 confirmations
         assert_array_result(self.nodes[1].listreceivedbylabel(),
                             {"label": label},