Fixed bugs found by psalm

Author: Nyholm

Filesystem.php

@@ -59,7 +59,7 @@ public function copy($originFile, $targetFile, $overwriteNewerFiles = false)
             }
 
             // Stream context created to allow files overwrite when using FTP stream wrapper - disabled by default
-            if (false === $target = @fopen($targetFile, 'w', null, stream_context_create(['ftp' => ['overwrite' => true]]))) {
+            if (false === $target = @fopen($targetFile, 'w', false, stream_context_create(['ftp' => ['overwrite' => true]]))) {
                 throw new IOException(sprintf('Failed to copy "%s" to "%s" because target file could not be opened for writing.', $originFile, $targetFile), 0, null, $originFile);
             }