[Filesystem] Fix str_contains deprecation

Author: NeilPeyssard

Diff for: Filesystem.php

@@ -199,7 +199,7 @@ private static function doRemove(array $files, bool $isRecursive): void
 
                     throw new IOException(sprintf('Failed to remove directory "%s": ', $file).$lastError);
                 }
-            } elseif (!self::box('unlink', $file) && (str_contains(self::$lastError, 'Permission denied') || file_exists($file))) {
+            } elseif (!self::box('unlink', $file) && ((self::$lastError && str_contains(self::$lastError, 'Permission denied')) || file_exists($file))) {
                 throw new IOException(sprintf('Failed to remove file "%s": ', $file).self::$lastError);
             }
         }