Use `getDisplayName` for roster contacts

src/converse-muc-views.js

@@ -2094,7 +2094,7 @@ converse.plugins.add('converse-muc-views', {
                     return;
                 }
                 form.addEventListener('submit', this.inviteFormSubmitted.bind(this), false);
-                const list = _converse.roster.map(i => ({'label': i.get('fullname') || i.get('jid'), 'value': i.get('jid')}));
+                const list = _converse.roster.map(i => ({'label': i.getDisplayName(), 'value': i.get('jid')}));
                 const el = this.el.querySelector('.suggestion-box').parentElement;
 
                 if (this.invite_auto_complete) {

src/headless/converse-muc.js

@@ -1560,7 +1560,7 @@ converse.plugins.add('converse-muc', {
                 result = true;
             } else {
                 // Invite request might come from someone not your roster list
-                contact = contact? contact.get('fullname'): Strophe.getNodeFromJid(from);
+                contact = contact? contact.getDisplayName(): Strophe.getNodeFromJid(from);
                 if (!reason) {
                     result = confirm(
                         __("%1$s has invited you to join a groupchat: %2$s", contact, room_jid)