Prevent crash

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

@@ -2327,6 +2327,7 @@ public class ServiceSynchronize extends ServiceBase implements SharedPreferences
                         @Override
                         public void delegate() {
                             try {
+                                if (cowner.value != null)
                                     cowner.value.destroy();
                             } catch (Throwable ex) {
                                 Log.e(ex);