fix: Add element existence check to prevent Page Builder crashes

Encountered a scenario where missing HTML elements in Page Builder caused runtime errors due to direct calls to setAttribute.

Added an existence check before setting attributes to avoid breaking the editor.

This ensures continued functionality and improves stability by handling cases where elements are not found.

Logically, the core should include such checks to enhance resilience and user experience.

Author: artttj

app/code/Magento/PageBuilder/view/adminhtml/web/js/stage-builder.js

@@ -58,7 +58,12 @@ function convertToInlineStyles(document: Document): void {
 
     _.each(viewportStyles, (styles, name: string) => {
         _.each(styles, (stylesArray: CSSStyleDeclaration[], selector: string) => {
-            const element: HTMLElement = document.querySelector(selector);
+            const element = document.querySelector<HTMLElement>(selector);
+
+            if (!element) {
+                console.error('Element not found for selector: %o. Unable to set attribute: "%s".', selector, `data-${name}-style`);
+                return;
+            }
 
             _.each(stylesArray, (style: CSSStyleDeclaration) => {
                 element.setAttribute(