fault_fragment_info.ilist is not set in dr_siginfo_t

`send_signal_to_client()` creates a `dr_siginfo_t` but does not initialise `fault_fragment_info.ilist` member so it contains garbage data when the `dr_siginfo_t` is passed to the client callback.

If possible this should be set to the actual ilist for the fragment but we need to at least initialise the field to `NULL`.