Fix wrong return value from wxWebViewIE::Find() in 64 bit build.

Fix wrong return value from wxWebViewIE::Find() in 64 bit build.

Using wxNOT_FOUND and an unsigned size() return value in the same operator ?:
resulted in wxNOT_FOUND being converted to an unsigned size_t type and while
converting it back to (signed) long worked in 32 bit builds where long and
size_t have the same size, it was broken in 64 bit builds where their sizes
are different.

Thanks g++ for catching this one.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74493 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775