emacs: Take advantage of position-remembering when returning to notmuch-hello

When we go into a search, and then later quit and return to the
notmuch-hello buffer, we want the point to remain in the same position
it was in when we left. So we have to call the position-remembering
notmuch-hello-update rather than notmuch-hello from the continuation.

emacs/notmuch-hello.el

@@ -193,7 +193,7 @@ diagonal."
 (defimage notmuch-hello-logo ((:type png :file "notmuch-logo.png")))
 
 (defun notmuch-hello-search-continuation()
-  (notmuch-hello t))
+  (notmuch-hello-update t))
 
 (defun notmuch-hello-update (&optional no-display)
   ;; Lazy - rebuild everything.