Update/Install: Reject invalid messages in the Shiny Updates postMessage handler.

This prevents conflicts with third-party messages (e.g. sent by browser extensions). The updates script expects a specific JSON-encoded message and now bails early if it's not valid JSON.

Fixes #37125.

git-svn-id: https://develop.svn.wordpress.org/trunk@37976 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/js/updates.js

@@ -2144,7 +2144,11 @@
 				return;
 			}
 
-			message = $.parseJSON( originalEvent.data );
+			try {
+				message = $.parseJSON( originalEvent.data );
+			} catch ( e ) {
+				return;
+			}
 
 			if ( 'undefined' === typeof message.action ) {
 				return;