Use wxCOMPtr throughout the wxWebViewIE Find code.

As well as making the code a bit neater this seems to fix some memory issues.

See #15207.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74020 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775