BUG/MINOR: stream-int: Don't block reads in si_update_rx() if chn may receive

BUG/MINOR: stream-int: Don't block reads in si_update_rx() if chn may receive

In si_update_rx() function, the reads may be blocked because we explicitly
don't want to read or because of a lack of room in the input buffer. The
first condition is valid. However the second one only test if the channel is
empty or not. It means the reads are blocked if there are still some output
data in the input channel, in its buffer or its pipe. This condition is not
accurate. The reads must not be blocked if the channel can still receive
data. Thus instead of relying on channel_is_empty() function, we now call
channel_may_recv().

This patch is especially useful to be able to catch read0 on client side
when we are waiting for a connection to the server, when abortonclose option
is enabled. Otherwise, the client abort is not detected.

This patch depends on "MINOR: channel: Rely on HTX version if appropriate in
channel_may_recv()". Both must be backported as far as 2.0 after a period of
observation to be sure nothing broke.