Prevent crash in FlxInputText when switching states (#3243)

Prevents null textField access in FlxInputText when switching between states. Resolves #3242.

flixel/text/FlxInputText.hx

@@ -482,6 +482,7 @@ class FlxInputText extends FlxText implements IFlxInputText
 	 */
 	override function destroy():Void
 	{
+		endFocus();
 		manager.unregisterInputText(this);
 
 		FlxDestroyUtil.destroy(onEnter);