This ensures that wxHtmlContainerCell height is set to some reasonable value
instead of 0 and fixes infinite loop which occurred in some circumstances in
wxGTL when trying to allocate size for wxHtmlListBox as it oscillated between
having a vertical scrollbar with bigger width and not having it with smaller
width. The latter was wrong as decreasing the width to 0 didn't really obviate
the need for the vertical scrollbar and was just an artefact due to not
setting wxHtmlContainerCell height at all in this case.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77663 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775