Bail out early from `esc_url()` if the URL becomes empty after stripping out disallowed characters.

Fixes #28015
Props jesin for the unit test

Built from https://develop.svn.wordpress.org/trunk@33923


git-svn-id: http://core.svn.wordpress.org/trunk@33892 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/formatting.php

@@ -3277,6 +3277,11 @@ function esc_url( $url, $protocols = null, $_context = 'display' ) {
 
 	$url = str_replace( ' ', '%20', $url );
 	$url = preg_replace('|[^a-z0-9-~+_.?#=!&;,/:%@$\|*\'()\\x80-\\xff]|i', '', $url);
+
+	if ( '' === $url ) {
+		return $url;
+	}
+
 	if ( 0 !== stripos( $url, 'mailto:' ) ) {
 		$strip = array('%0d', '%0a', '%0D', '%0A');
 		$url = _deep_replace($strip, $url);

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-33922';
+$wp_version = '4.4-alpha-33923';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.