close db connection before delivering file. Also make sure connection can't be closed twice.

git-svn-id: file:///svn/phpbb/branches/phpBB-3_0_0@8772 89ea8834-ac86-4346-8a33-228a782c2dd0

phpBB/download/file.php

@@ -479,6 +479,10 @@ function send_file_to_browser($attachment, $upload_dir, $category)
 	{
 		header("Content-Length: $size");
 	}
+
+	// Close the db connection before sending the file
+	$db->sql_close();
+
 	if (!set_modified_headers($attachment['filetime'], $user->browser))
 	{
 		// Try to deliver in chunks