Fix scroll history to down with unread bar.

Regression was introduced in 972b5078f6.

When we show history at a specific message or at unread messages we
need to clear and destroy old showFrom and unreadBar like it is done
in historyLoaded(), otherwise we always scroll to existing unreadBar.

Telegram/SourceFiles/historywidget.cpp

@@ -1794,6 +1794,9 @@ void HistoryWidget::showHistory(const PeerId &peerId, MsgId showAtMsgId, bool re
 
 				setMsgId(showAtMsgId);
 				if (_historyInited) {
+					countHistoryShowFrom();
+					destroyUnreadBar();
+
 					auto item = getItemFromHistoryOrMigrated(_showAtMsgId);
 					animatedScrollToY(countInitialScrollTop(), item);
 					highlightMessage(item);