FIX: grid may be not updated when right clicking on macOS

Author: rich2014

src/fileviews/ufileviewwithmainctrl.pas

@@ -965,6 +965,9 @@ procedure TFileViewWithMainCtrl.MainControlMouseDown(Sender: TObject; Button: TM
 {$IF DEFINED(LCLWIN32)}
   FMouseFocus:= MainControl.Focused;
   SetFocus;
+{$ELSEIF DEFINED(LCLCOCOA)}
+  FMouseFocus:= MainControl.Focused;
+  MainControl.Invalidate;
 {$ELSE}
   FMouseFocus := not FMouseEnter;
   FMouseEnter := False;