Fix stack overflow crash in emoji panel hiding.

A call to hideChildren before setting _hiding to the desired value
could lead through leaveEvent to a recursive call to hideAnimated.

Telegram/SourceFiles/chat_helpers/tabbed_panel.h

@@ -77,7 +77,7 @@ private:
 	QImage grabForAnimation();
 	void startShowAnimation();
 	void startOpacityAnimation(bool hiding);
-	void prepareCache();
+	void prepareCacheFor(bool hiding);
 
 	void opacityAnimationCallback();