Fix changing tabs marking conversation read

ts/state/ducks/conversations.ts

@@ -3947,6 +3947,8 @@ function showConversation({
 
     if (nav.selectedNavTab !== NavTab.Chats) {
       dispatch(navActions.changeNavTab(NavTab.Chats));
+      const conversation = window.ConversationController.get(conversationId);
+      conversation?.setMarkedUnread(false);
     }
 
     if (conversationId === conversations.selectedConversationId) {

ts/state/smart/ChatsTab.tsx

@@ -79,16 +79,16 @@ export function SmartChatsTab(): JSX.Element {
       scrollToMessage(selectedConversationId, targetedMessage);
     }
 
-    if (!selectedConversationId) {
+    if (
-      return;
+      selectedConversationId != null &&
+      selectedConversationId !== prevConversationId
+    ) {
+      const conversation = window.ConversationController.get(
+        selectedConversationId
+      );
+      strictAssert(conversation, 'Conversation must be found');
+      conversation.setMarkedUnread(false);
     }
-
-    const conversation = window.ConversationController.get(
-      selectedConversationId
-    );
-    strictAssert(conversation, 'Conversation must be found');
-
-    conversation.setMarkedUnread(false);
   }, [
     onConversationClosed,
     onConversationOpened,