Filesystem API: Check for the correct result in some WP_Filesystem_FTPext methods.

This avoids a PHP warning when `::dirlist()` returns `false` under certain conditions:

> `Warning: Trying to access array offset on value of type bool in wp-admin/includes/class-wp-filesystem-ftpsockets.php on line 326`

Follow-up to [6779], [30678], [45226].

Props apermo, malt3, SergeyBiryukov.
Fixes #63474.

git-svn-id: https://develop.svn.wordpress.org/trunk@61311 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-admin/includes/class-wp-filesystem-ftpext.php

@@ -299,7 +299,7 @@ public function chmod( $file, $mode = false, $recursive = false ) {
 	public function owner( $file ) {
 		$dir = $this->dirlist( $file );
 
-		return $dir[ $file ]['owner'];
+		return $dir[ $file ]['owner'] ?? '';
 	}
 
 	/**
@@ -313,7 +313,7 @@ public function owner( $file ) {
 	public function getchmod( $file ) {
 		$dir = $this->dirlist( $file );
 
-		return $dir[ $file ]['permsn'];
+		return $dir[ $file ]['permsn'] ?? '';
 	}
 
 	/**
@@ -327,7 +327,7 @@ public function getchmod( $file ) {
 	public function group( $file ) {
 		$dir = $this->dirlist( $file );
 
-		return $dir[ $file ]['group'];
+		return $dir[ $file ]['group'] ?? '';
 	}
 
 	/**

src/wp-admin/includes/class-wp-filesystem-ftpsockets.php

@@ -309,7 +309,7 @@ public function chmod( $file, $mode = false, $recursive = false ) {
 	public function owner( $file ) {
 		$dir = $this->dirlist( $file );
 
-		return $dir[ $file ]['owner'];
+		return $dir[ $file ]['owner'] ?? '';
 	}
 
 	/**
@@ -323,7 +323,7 @@ public function owner( $file ) {
 	public function getchmod( $file ) {
 		$dir = $this->dirlist( $file );
 
-		return $dir[ $file ]['permsn'];
+		return $dir[ $file ]['permsn'] ?? '';
 	}
 
 	/**
@@ -337,7 +337,7 @@ public function getchmod( $file ) {
 	public function group( $file ) {
 		$dir = $this->dirlist( $file );
 
-		return $dir[ $file ]['group'];
+		return $dir[ $file ]['group'] ?? '';
 	}
 
 	/**