Slightly improve best size calculation for wxListCtrl with wxLC_NO_HEADER.

Slightly improve best size calculation for wxListCtrl with wxLC_NO_HEADER.

Use some arbitrary but relatively large width and height instead of falling
back to wxControlBase best size computation which, at least in wxGTK, simply
returns (1, 1) resulting in list control of unusably small size.

This is, of course, still far from ideal and we should really use the items to
calculate the best width but it at least allow the list control in the generic
log dialog to be shown correctly in wxGTK.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71733 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775