fix OutOfBoundsException when using mail or sendmail transport
merged branch csanquer/master (PR #42)

This PR was squashed before being merged into the master branch (closes #42).

Discussion
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fix OutOfBoundsException when using mail or sendmail transport

Hi,

Since the symfony/SwiftmailerBundle#34 had been merged, an exception occured when using mail or sendmail transport :

```
[Symfony\Component\DependencyInjection\Exception\OutOfBoundsException]
  The index "1" is not in the range [0, 0].
```

This patch fix it.

Commits
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01fb626 fix OutOfBoundsException when using mail or sendmail transport