Prevent closing modal when templates are still loading

[MAILPOET-6049]

mailpoet/assets/js/src/email-editor/engine/components/template-select/select-modal.tsx

@@ -30,6 +30,7 @@ export function SelectTemplateModal({ onSelectCallback }) {
     const blankTemplate = templates.find(
       (template) => template.slug === BLANK_TEMPLATE,
     );
+    if (!blankTemplate) return; // Prevent close if blank template is still not loaded
     handleTemplateSelection(blankTemplate);
   };