Fall back on ::GetMessagePos() if ::GetCursorPos() fails under MSW.

In some rare but reproducible cases GetCursorPos() can fail and return without
filling in the provided point. Fall back to GetMessagePos() if this happens:
this is not ideal but clearly better than using uninitialized position or hard
coding something like (0, 0).

Closes #13664.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69758 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/treectrl.cpp

@@ -3645,7 +3645,7 @@ bool wxTreeCtrl::MSWOnNotify(int idCtrl, WXLPARAM lParam, WXLPARAM *result)
         case NM_RCLICK:
             {
                 TV_HITTESTINFO tvhti;
-                ::GetCursorPos(&tvhti.pt);
+                wxGetCursorPosMSW(&tvhti.pt);
                 ::ScreenToClient(GetHwnd(), &tvhti.pt);
                 if ( TreeView_HitTest(GetHwnd(), &tvhti) )
                 {