Fix VC6 compilation after r73880.

Work around the broken scoping for the variables declared inside for loops in
this compiler by declaring the loop variable once for all loops.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73881 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775