Use wxWebKitNewWindowEventHandler to perform a proper static_cast<>, which
detects incorrect casts during compilation, instead of
wxWebKitNewWindowEventFunction which was just doing an unsafe C-style cast.
Cloes #13805.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70108 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775