Fix an assertion failure seen on the layout tests, and when closing the window after...

Fix an assertion failure seen on the layout tests, and when closing the window after visiting <coudal.com/losalamos/>.

Reviewed by Oliver Hunt.

* Plugins/WebBaseNetscapePluginStream.mm:
(-[WebBaseNetscapePluginStream _destroyStream]): Unlink the file and close the file
descriptor even when the stream is being destroyed without the load completing. This
avoids leaking the path and file descriptor, and leaving the temporary file on disk.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@28136 268f45cc-cd09-0410-ab3c-d52691b4dbfc