select_cancel_all could prematurely clean a select table slot that was
still initializing in do_select. This can happen when two select calls
are active and operating on the same file(s). One select is still
initializing in do_select, the other receives a postponed result
(select_reply2). The handler for the postponed result would cancel all
selects that were operating on the same file it got a result for.
Consequently, the initializing select suddenly has no valid file pointers
in its slot anymore, and causes null dereferences.
Change-Id: I647de9889a0548c4d232309cd5cd27165ef6ebbf
17c8162011