usability improvements to autocomplete ("no results" etc.), needs refactoring

src/public/javascripts/dialogs/jump_to_note.js

@@ -23,7 +23,18 @@ async function showDialog() {
         source: async function(request, response) {
             const result = await server.get('autocomplete?query=' + encodeURIComponent(request.term));
 
-            response(result);
+            if (result.length > 0) {
+                response(result);
+            }
+            else {
+                response([{
+                    label: "No results",
+                    value: "No results"
+                }]);
+            }
+        },
+        focus: function(event, ui) {
+            return $(ui.item).val() !== 'No results';
         },
         minLength: 2
     });