fix(embed): make tabs in colorbox popup usable

Function embed_select_tab expects input page to be set, but it isn't.
Adding a
´´´
set_input('page', $page[1]);
´´´
to the embed_page_handler function fixes this

Refs: Issue #6357
Merge pull request #6363 from slyhne/patch-6

fix(embed): make tabs in colorbox popup usable