Fix search binding regression introduced in
1be1228
From the ticket:
After
1be1228, when a previous search pattern exists, :/ and :? do
not set a new search pattern, and thus function like n and N. This
breaks search bindings since they must use :/ and :? instead of /
and ? (which still work). For example, the default bind diff @ :/^@@
does not work correctly following a search for a different pattern.
To reproduce: Search /foo and then search :/bar (note :/, not /),
for any distinct foo and bar.
This is fixed by ensuring that the search is reset when
`view->env->search` is updated by the prompt code.
Fixes #476