IDLE when supported only

app/src/main/java/eu/faircode/email/ServiceSynchronize.java

@@ -589,6 +589,7 @@ public class ServiceSynchronize extends LifecycleService {
                     noops.add(noop);
 
                     // Receive folder events
+                    if (istore.hasCapability("IDLE")) {
                         Thread idle = new Thread(new Runnable() {
                             @Override
                             public void run() {
@@ -616,6 +617,7 @@ public class ServiceSynchronize extends LifecycleService {
                         idle.start();
                         idlers.add(idle);
                     }
+                }
 
                 BroadcastReceiver processReceiver = new BroadcastReceiver() {
                     @Override