Minor fixes after last commit:

Minor fixes after last commit:
1. don't pass -1 to base class DoSetSize(), this is documented to not work
   under Win2k
2. instead, don't do anything at all if neither size nor position changed
3. only call DoGetSize() once instead of doing it in both if branches
4. added comment about 30000 returned by CB_GETDROPPEDCONTROLRECT

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@38308 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775