Don't use any icon for items inserted without one in wxMSW wxListCtrl.

Don't use any icon for items inserted without one in wxMSW wxListCtrl.

Previously we erroneously used the first icon in the image list for them
instead. This was inconsistent with wxGTK and didn't make much sense, even if
it is the default behaviour of the native control, so don't do this any more
and explicitly specify I_IMAGENONE for the icon if it wasn't given.

Closes #15421.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74716 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775