Use url helper for TopicalEvent#search_index
Use url helper for TopicalEvent#search_index

It was crashing when doing a full index rebuild with:

undefined method `topical_event_path' for #<TopicalEvent:0x0000000df68cd8>
app/models/topical_event.rb:89:in `search_link'

ggoral/whitehall,YOTOV-LIMITED/whitehall,hotvulcan/whitehall,askl56/whitehall,YOTOV-LIMITED/whitehall,hotvulcan/whitehall,YOTOV-LIMITED/whitehall,ggoral/whitehall,YOTOV-LIMITED/whitehall,alphagov/whitehall,askl56/whitehall,askl56/whitehall,ggoral/whitehall,alphagov/whitehall,hotvulcan/whitehall,alphagov/whitehall,ggoral/whitehall,robinwhittleton/whitehall,robinwhittleton/whitehall,askl56/whitehall,hotvulcan/whitehall,alphagov/whitehall,robinwhittleton/whitehall,robinwhittleton/whitehall