just return the min size needed by the sizer for the windows with sizers from their...

just return the min size needed by the sizer for the windows with sizers from their DoGetBestSize() instead of adjusting it upwards to the current size via GetWindowSizeForVirtualSize() call: this might be wrong as it could reintroduce the bug fixed in rev 1.66 of src/generic/scrlwing.cpp (but it's not really clear just what exactly this bug was) but the existing code was definitely wrong as the best size of the window must not change as it's being resized

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@45864 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775