Media: Check if content URL includes a hostname in `wp_calculate_image_srcset()`.

This resolves an `Undefined array key "host"` PHP warning if `WP_CONTENT_URL` is set to a relative URL.

Follow-up to [58097].

Reviewed by hellofromTonya.
Merges [58773] to the 6.6 branch.

Props mattraines, narenin, pamprn, SergeyBiryukov.
Fixes #61690.
Built from https://develop.svn.wordpress.org/branches/6.6@58862


git-svn-id: http://core.svn.wordpress.org/branches/6.6@58258 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/media.php

@@ -1366,13 +1366,17 @@ function wp_calculate_image_srcset( $size_array, $image_src, $image_meta, $attac
 	 * (which is to say, when they share the domain name of the current request).
 	 */
 	if ( is_ssl() && ! str_starts_with( $image_baseurl, 'https' ) ) {
-		// Since the `Host:` header might contain a port we should
-		// compare it against the image URL using the same port.
+		/*
+		 * Since the `Host:` header might contain a port, it should
+		 * be compared against the image URL using the same port.
+		 */
 		$parsed = parse_url( $image_baseurl );
-		$domain = $parsed['host'];
+		$domain = isset( $parsed['host'] ) ? $parsed['host'] : '';
+
 		if ( isset( $parsed['port'] ) ) {
 			$domain .= ':' . $parsed['port'];
 		}
+
 		if ( $_SERVER['HTTP_HOST'] === $domain ) {
 			$image_baseurl = set_url_scheme( $image_baseurl, 'https' );
 		}

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.6.2-alpha-58861';
+$wp_version = '6.6.2-alpha-58862';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.