Limit wxListBox best size to 100x100. Particularly important on trunk where

Limit wxListBox best size to 100x100.  Particularly important on trunk where
the best size is not cached and will thus keep telling the sizers that the
best size is the full size of the content (i.e. such that you wouldn't need
to scroll it).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@51894 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775