Fix a bug where calypsoifyGutenberg was undefined (#37900)

We tried to reference the global declaration even though it was undefined.

To fix, we reference it directly from the window object, which declares
a variable and sets its value to undefined.

apps/full-site-editing/full-site-editing-plugin/full-site-editing/plugins/close-button-override/index.js

@@ -1,5 +1,4 @@
 /* global fullSiteEditing */
-/* global calypsoifyGutenberg */
 
 /**
  * External dependencies
@@ -66,6 +65,13 @@ domReady( () => {
 		// These should go here so that they have any updates that happened while querying for the selector.
 		let { closeButtonLabel, closeButtonUrl } = fullSiteEditing;
 
+		/**
+		 * We have to reference calypsoifyGutenberg off of the window object
+		 * directly to handle the case where it is undefined. Otherwise, the
+		 * variable declariation itself won't exist, causing a runtime error.
+		 */
+		const { calypsoifyGutenberg } = window;
+
 		// Use wpcom close button/url if they exist.
 		if ( calypsoifyGutenberg && calypsoifyGutenberg.closeUrl ) {
 			closeButtonUrl = calypsoifyGutenberg.closeUrl;