Test of possibly unassigned setting in _filter_html_tips

_filter_html_tips() accesses $filter->settings['allowed_html'] without first checking whether that key exists.

As soon as the filtered html text format has been configured, it exists and the problem goes away, but on a fresh install this test fails with a notice.

One possible patch is suggested, which checks for the missing key before using it. It might be yet more valuable to initialize the settings and get rid of the existing (incomplete) test or the proposed (better) one, though ?