dont update on every single block (#776)

app/src/main/java/com/m2049r/xmrwallet/service/WalletService.java

@@ -108,11 +108,15 @@ public class WalletService extends Service {
             Timber.d("unconfirmedMoneyReceived() %d @ %s", amount, txId);
         }
 
-        int lastTxCount = 0;
+        private long lastBlockTime = 0;
+        private int lastTxCount = 0;
 
         public void newBlock(long height) {
             final Wallet wallet = getWallet();
             if (wallet == null) throw new IllegalStateException("No wallet!");
+            // don't flood with an update for every block ...
+            if (lastBlockTime < System.currentTimeMillis() - 2000) {
+                lastBlockTime = System.currentTimeMillis();
                 Timber.d("newBlock() @ %d with observer %s", height, observer);
                 if (observer != null) {
                     boolean fullRefresh = false;
@@ -132,6 +136,7 @@ public class WalletService extends Service {
                         observer.onRefreshed(wallet, fullRefresh);
                 }
             }
+        }
 
         public void updated() {
             Timber.d("updated()");