Add requestPersistence call at TradeTask.complete call.

This is not really needed as we call it at each state change of the
trade but gives more redundancy in case we missed one or once
changes are applied and a dev forgets to call it.

Multiple repeated calls do have close to zero costs.

core/src/main/java/bisq/core/trade/protocol/tasks/TradeTask.java

@@ -37,6 +37,13 @@ public abstract class TradeTask extends Task<Trade> {
         processModel = trade.getProcessModel();
     }
 
+    @Override
+    protected void complete() {
+        processModel.getTradeManager().requestPersistence();
+
+        super.complete();
+    }
+
     @Override
     protected void failed() {
         trade.setErrorMessage(errorMessage);