Pass model's whole JSON to nickname form

Not strictly necessary for vanilla Converse, but makes life easier
downstream

src/converse-muc-views.js

@@ -1103,14 +1103,14 @@ export const ChatRoomView = ChatBoxView.extend({
      * @method _converse.ChatRoomView#renderNicknameForm
      */
     renderNicknameForm () {
-        const tmp_result = tpl_muc_nickname_form(this.model.get('nick'));
+        const tpl_result = tpl_muc_nickname_form(this.model.toJSON());
         if (api.settings.get('muc_show_logs_before_join')) {
             const container = this.el.querySelector('.muc-bottom-panel');
-            render(tmp_result, container);
+            render(tpl_result, container);
             u.addClass('muc-bottom-panel--nickname', container);
         } else {
             const form = this.el.querySelector('.muc-nickname-form');
-            const form_el = u.getElementFromTemplateResult(tmp_result);
+            const form_el = u.getElementFromTemplateResult(tpl_result);
             if (form) {
                 sizzle('.spinner', this.el).forEach(u.removeElement);
                 form.outerHTML = form_el.outerHTML;

src/templates/muc_nickname_form.js

@@ -3,7 +3,7 @@ import { api } from "@converse/headless/converse-core";
 import { html } from "lit-html";
 
 
-export default (nickname) => {
+export default (o) => {
     const i18n_nickname =  __('Nickname');
     const i18n_join = __('Enter groupchat');
     const i18n_heading = api.settings.get('muc_show_logs_before_join') ?
@@ -15,7 +15,7 @@ export default (nickname) => {
             <form class="converse-form chatroom-form converse-centered-form">
                 <fieldset class="form-group">
                     <label>${i18n_heading}</label>
-                    <input type="text" required="required" name="nick" value="${nickname || ''}"
+                    <input type="text" required="required" name="nick" value="${o.nick || ''}"
                         class="form-control" placeholder="${i18n_nickname}"/>
                 </fieldset>
                 <fieldset class="form-group">