Fix history loop issue with /search

When an error occurs on the route /search, it defaults back to index
page.  But this error will happen with any bare (no params) search, so
you can get into a loop where the back button is constantly re-pushing
the index-page.
This now replaces the history entry on error, which should fix it.

src/js/apps/discovery/router.js

@@ -126,7 +126,7 @@ define([
           );
         }
       } else {
-        this.getPubSub().publish(this.getPubSub().NAVIGATE, 'index-page');
+        this.getPubSub().publish(this.getPubSub().NAVIGATE, 'index-page', { replace: true });
       }
     },