BUG/MEDIUM: mux-h2: fix early close with option abortonclose

BUG/MEDIUM: mux-h2: fix early close with option abortonclose

Olivier found that commit 99ad1b3e8 ("MINOR: mux-h2: stop relying on
CS_FL_REOS") managed to break abortonclose again with H2. What happens
is that while the CS_FL_REOS flag was set on some transitions to the
HREM state, it's not set on all and is in fact only set when the low
level connection is closed. So making the replacement condition match
the HREM and ERROR states is not correct and causes completely correct
requests to send advertise an early close of the connection layer while
only the stream's input is closed.

In order to avoid this, we now properly split the checks for the CLOSED
state and for the closed connection. This way there is no risk to set
the EOS flag too early on the connection.

No backport is needed.