Fix wrong in wxListCtrl::SetItemColumnImage() in r74716.

The check for "image == -1" was added to a wrong line.

See #15421.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74780 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775