Remove stream filters in Stream destructor only if they are still valid resources

[crocodele]

When a Reader or Writer has a stream filter and the handle to the stream is closed manually in code, there's a fatal error in the Stream destructor.

To reproduce: in current master branch, the test case in the PR fails with a fatal error in the Stream destructor:

PHP Fatal error:  Uncaught TypeError: stream_filter_remove(): supplied resource is not a valid stream filter resource in /path/to/example/vendor/league/csv/src/Stream.php:84
Stack trace:
#0 /path/to/example/vendor/league/csv/src/Stream.php(84): stream_filter_remove()
#1 [internal function]: League\Csv\Stream->League\Csv\{closure}()
#2 /path/to/example/vendor/league/csv/src/Stream.php(84): array_walk_recursive()
#3 [internal function]: League\Csv\Stream->__destruct()
#4 {main}
  thrown in /path/to/example/vendor/league/csv/src/Stream.php on line 84

[nyamsprod]

Thanks for finding and fixing the bug. Nice catch. I will merge the PR but I update or improve if needed your fix.

[nyamsprod]

version 9.20.1 is released with you fix included. Thanks again