BUG/MEDIUM: h2: Make sure we set send_list to NULL in h2_detach().

In h2_detach(), if we still have a send_wait pointer, because we woke the
tasklet up, but it hasn't ran yet, explicitely set send_wait to NULL after
we removed the tasklet from the task list.
Failure to do so may lead to crashes if the h2s isn't immediately destroyed,
because we considered there were still something to send.

This should be backported to 1.9.
1 file changed