(core) Tweak autocomplete to only suggest team members

Summary: This changes the suggestions in the User Manager autocomplete.

Test Plan: Project tests.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3656

app/client/lib/ACUserManager.ts

@@ -83,7 +83,7 @@ export function buildACMemberEmail(
       .filter(item => item.cleanText.includes(cleanText))
       .sort((a, b) => a.cleanText.localeCompare(b.cleanText));
     results.items = items;
-    if (!results.items.length) {
+    if (!results.items.length && cleanText) {
       const newObject = {
         value: text,
         cleanText,