Improved logic in ComboBox.SelectFirstItem.

static/plugin_dbui/src/form/field/ComboBox.js

@@ -70,7 +70,9 @@ Ext.define('App.form.field.ComboBox', {
 
         var record;
 
+        // the store is not ready, reschedule the request
         if (!this.store.getCount()) {
+            this.store.on('load', this.selectFirstItem, this, {single: true});
             return;
         }