Don't present multiple converastion views ever.

Signal/src/ViewControllers/HomeView/HomeViewController.m

@@ -928,6 +928,9 @@ NSString *const kArchivedConversationsReuseIdentifier = @"kArchivedConversations
         [mvc configureForThread:thread action:action];
         self.lastThread = thread;
 
+        // Never push more than one conversation view controller at a time.
+        [self.navigationController popToViewController:self animated:NO];
+
         [self pushTopLevelViewController:mvc animateDismissal:YES animatePresentation:YES];
     });
 }