Fix progress feel over messages in Conversation view

Unlike with many other lists,
we are not clearing the list of private messages when restarting the activity.
We still load the messages from the database and add them to the view.
When there are no new message to add,
the usual insert observers do not trigger
and we do not call list.showData() although we should.
Doing so removes the progress bar as soon as messages have been loaded.

briar-android/src/main/java/org/briarproject/briar/android/contact/ConversationActivity.java

@@ -378,8 +378,8 @@ public class ConversationActivity extends BriarActivity
 				textInputView.setSendButtonEnabled(true);
 				List<ConversationItem> items = createItems(headers,
 						introductions, invitations);
-				if (items.isEmpty()) list.showData();
-				else adapter.addAll(items);
+				adapter.addAll(items);
+				list.showData();
 				// Scroll to the bottom
 				list.scrollToPosition(adapter.getItemCount() - 1);
 			} else {