added null checks to new messages listener

chatto/src/main/javascript/ts/src/view/UserView.ts

@@ -125,7 +125,7 @@ export class UserView implements Observer<ActiveUserViewModel> {
         // this._chatModel.getMessages(userName, vm.passphrase, null, "new");
         el.className += " active";
         log.debug("loop", this._newMessagesLoop)
-        if (vm.unlocked) {
+        if (vm.unlocked && vm.lastMessageTime != null) {
             this._newMessagesLoop = setInterval(this._chatModel.getMessages.bind(this._chatModel,
                 vm, "update"), 10_000);
         }
@@ -135,8 +135,10 @@ export class UserView implements Observer<ActiveUserViewModel> {
         // vms.filter(v => v.userName == vm.userName).map(v => v.userName = vm.userName)
         log.debug(vms)
 
-        this._newMessagesLoop = setInterval(this._chatModel.getMessages.bind(this._chatModel,
-            vm, "update"), 10_000);
+        if (vm.lastMessageTime != null) {
+            this._newMessagesLoop = setInterval(this._chatModel.getMessages.bind(this._chatModel,
+                vm, "update"), 10_000);
+        }
         this._model.notify();
     }