There's a long-standing bug in select. If we have poll-only
descriptors in the fd set, select overwrites the incoming
fd sets with the polling result. If none of the fds is ready,
select has to loop again. But now the fd sets are set to all
zero and select hangs.
Fix this by utilizing the local fd sets r, w, e as storage for
the incoming fd sets and use them to initialize select_stuff.
If we have to loop, overwritung the incoming fd sets doesn't matter.
While at it, rename r, w, e to readfds_in, writefds_in, exceptfds_in.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
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