Fix wxPGProperty::SetChoiceSelection

When selected choice is changed then set as selected value the value corresponding to the new index, not the index itself.

Closes #16401.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76971 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775