Fix some remaining usage of local InputManager instances

osu.Game/Overlays/ChatOverlay.cs

@@ -243,7 +243,7 @@ namespace osu.Game.Overlays
         protected override void OnFocus(InputState state)
         {
             //this is necessary as inputTextBox is masked away and therefore can't get focus :(
-            InputManager.ChangeFocus(inputTextBox);
+            GetContainingInputManager().ChangeFocus(inputTextBox);
             base.OnFocus(state);
         }