[FIX] web: properly set page data in 'ModelFieldSelector' widget

When passing a default field chain to ModelFieldSelector, the page data is
not set correctly for the relational field. To understand the issue :

- login to v11 enterprise all db branch in runbot (debug mode recommended)
- create a mass mailing, add subject, select 'Contact' in `Recipients` field
- click on domain selector and select 'Company' from ModelFieldSelector popover
- click somewhere else to close the popover
- again open domain selector and observe the popover

Current behavior : fields of  `Contact` are visible in the page even thogh
                   `Company` is selected in the ModelFieldSelector
Expected behavior : fields of `Company` should be visible

This commit fixes the issue by correctly pushing the page data
in ModelFieldSelector.

task - 2058702

closes odoo/odoo#47231

X-original-commit: 5746c2705c324b124445f38ead4f75624b3f99e3
Related: odoo/enterprise#9124
Signed-off-by: Damien Bouvy (dbo) <dbo@odoo.com>

addons/web/static/src/js/widgets/model_field_selector.js

@@ -303,8 +303,12 @@ var ModelFieldSelector = Widget.extend({
         function processChain(chain) {
             var fieldName = chain.pop();
             var field = this._getLastPageField(fieldName);
-            if (field && field.relation && chain.length > 0) { // Fetch next chain node if any and possible
-                return this._pushPageData(field.relation).then(processChain.bind(this, chain));
+            if (field && field.relation) {
+                if (chain.length) { // Fetch next chain node if any and possible
+                    return this._pushPageData(field.relation).then(processChain.bind(this, chain));
+                } else { // Simply update the last popover page
+                    return this._pushPageData(field.relation);
+                }
             } else if (field && chain.length === 0) { // Last node fetched
                 return Promise.resolve();
             } else if (!field && fieldName === "1") { // TRUE_LEAF