As it currently stands, after the introduction of operators, narrowing
to messages that contained X would also trigger a find-in-page.
This stops that from happening, and then also makes the default action
of the search-bar-invoked-without-a-typeahead be 'narrow to messages
containing x' rather than 'find in page'.
(imported from commit 1beffce426c6b00449e7c1c803687a129747ed63)