Correct wxMSW wxToolTip behaviour for wxRadioBox items tooltips.

Correct wxMSW wxToolTip behaviour for wxRadioBox items tooltips.

The assert added in r66053 checking that we couldn't have tooltips for child
windows if we didn't have the tooltip for the main one turned out to be wrong,
at least in wxRadioBox case it's perfectly possible to have the tooltips for
the individual radio buttons without having one for the box itself.

Replace the assert with a simple if check.

This fixes a unit test failure in RadioBoxTestCase.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66169 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775