Don't leave orphan taskbar icon window alive if setting it up fails.

Don't leave orphan taskbar icon window alive if setting it up fails.

This fixes a rare bug which happens when we fail to install the task bar icon
under MSW for whatever reason (the only known way to reproduce it is to try to
do it very quickly after resume from suspend but there might be other
situations in which this happens). In this case we must delete the icon as we
are not going to get any timeout expiration notifications for it and so if we
don't delete it immediately, it would remain alive forever, preventing the
application from exiting as it counts as a top level window.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72917 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775