Fixed drawing a check box in the undetermined state for non-themed MSW apps.

Fixed drawing a check box in the undetermined state for non-themed MSW apps.

wxRendererMSW::DoDrawFrameControl (used for systems prior to XP or when theming is disabled) didn't check for the wxCONTROL_UNDETERMINED flag yet. Set the appropriate styles when the flag is used to fix drawing check boxes in their third state (as used in for example the treelist sample).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68951 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775