Fix File descriptor leak related to GH-1324.

Following my comment on the code, here is the fix for issue #1324 !


Thanks @FooBarWidget for your work !

Before fix
====

```
> ab -n 1000 -c 10 http://localhost &
> # Waiting a couple of seconds
> lsof | grep -i passenger-error | wc -l
495
```


After fix
====

```
> ab -n 1000 -c 10 http://localhost &
> # Waiting a couple of seconds
> lsof | grep -i passenger-error | wc -l
0
```