Update lost password URL for WP 4.4 compatibility

#8100

includes/login-register.php

@@ -200,10 +200,21 @@ function edd_login_register_error_message( $errors, $redirect ) {
  * @return string
  */
 function edd_get_lostpassword_url() {
-	$url = wp_get_raw_referer();
+	$url = false;
+	// `wp_get_raw_referer` was added in WP 4.5; this check is required as we still support 4.4.
+	if ( function_exists( 'wp_get_raw_referer' ) ) {
+		$url = wp_get_raw_referer();
+	} else {
+		if ( ! empty( $_REQUEST['_wp_http_referer'] ) ) {
+			$url = wp_unslash( $_REQUEST['_wp_http_referer'] );
+		} elseif ( ! empty( $_SERVER['HTTP_REFERER'] ) ) {
+			$url = wp_unslash( $_SERVER['HTTP_REFERER'] );
+		}
+	}
 	if ( empty( $url ) ) {
 		$url = edd_get_checkout_uri();
 	}
+	$url      = wp_validate_redirect( $url );
 	$redirect = add_query_arg(
 		array(
 			'checkemail'         => 'confirm',