Assert if an invalid column index is specified when inserting wxListCtrl item.

Assert if an invalid column index is specified when inserting wxListCtrl item.

This also catches the case of inserting an item in a report mode wxListCtrl
without adding any columns to it first. Previously this did result in an
assert but with a less clear error message and, most importantly, still a
crash afterwards. Assert only now, don't crash.

The message could still be improved but hopefully people will be able to
understand that inserting items when no columns are defined is not the right
thing to do.

Closes #12119.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64473 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775