Occasional errors with zlib.output_compression = On

Hello, occasionally I experience this error when I should not be seeing any whoops-related pages.

Uncaught Whoops\Exception\ErrorException: ob_end_clean(): failed to discard buffer of zlib output compression (1)

I've identified the issue is caused by Run.php line 396:

while ($this->system->getOutputBufferLevel() > 0) {
    $this->system->endOutputBuffering();
}

I am also submitting a PR with a very simple fix