improve invite error handling (#2649)

* fix(invite): do not send empty queries for people search

The endpoint might return an error if an empty query is sent.

* fix(invite): add error logging for failed people directory requests

The error currently being passed through from $.getJSON ended up
being an empty string plus was not getting logged. So switch to
fetch to move along with jquery killing and log the error.

* fix(dial-in): add error logging for failed requests

* ref(invite): create a fetch helper to remove duplicate logic

react/features/invite/components/AddPeopleDialog.web.js

@@ -568,7 +568,7 @@ class AddPeopleDialog extends Component<*, *> {
 
         let peopleSearchPromise;
 
-        if (this.props.enableAddPeople) {
+        if (this.props.enableAddPeople && text) {
             peopleSearchPromise = searchDirectory(
                 _peopleSearchUrl,
                 _jwt,