Don't let `:let &hlsearch=1` show up after failed search
Don't let `:let &hlsearch=1` show up after failed search

Try a search which looks in a non-existent directory:

  :Ack foo bar

Or a search that won't find any results:

  :Ack foobarbazzzzzzzzzzzzzz

Both of these were leaving the `:let` command visible on the
command-line[*]. Hide it by running an empty `:echo`.

[*] This wasn't entirely reliable for me. Vim has funny redrawing rules,
so I wasn't always able to repro this issue before this commit.

wincent/ferret