FlySpray: enable comments on closed issues

[Mathias Kresin]

With the current FlySpray configuration it isn't possible to add a
comment to a closed issue. This way it isn't possible to provide more
information while "Request re-open case".

In my case the issue was closed but the bug only partially fixed and
there was no way of adding these informations to the bugreport.

In my opinion, comments to closed issues should be allowed.

Mathias