Fix incorrect code sorting pages by their widths in wxRibbon.

Fix incorrect code sorting pages by their widths in wxRibbon.

The "sneaky obj array trickery" wasn't very sneaky but was just plain wrong
and misused object array of pages in a way that was invalid and didn't crash
just because of sheer luck.

Rewrite this code to use a temporary wxVector of pages that can be sorted
independently of the main m_pages array. This is 100% safe and also more
clear.

Closes #14625.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72516 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775