BUG/MINOR: mux-h1: Don't report an error on EOS if no message was received

An error is reported if the EOS is detected before the end of the message. But
we must be carefull to not report an error if there is no message at all.

This patch must be backported to 1.9.
diff --git a/src/mux_h1.c b/src/mux_h1.c
index 5978405..c09d008 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -1393,7 +1393,7 @@
 
 	if ((h1s->cs->flags & CS_FL_REOS) && (!b_data(&h1c->ibuf) || htx_is_empty(htx))) {
 		h1s->cs->flags |= CS_FL_EOS;
-		if (h1m->state < H1_MSG_DONE)
+		if (h1m->state > H1_MSG_LAST_LF && h1m->state < H1_MSG_DONE)
 			h1s->cs->flags |= CS_FL_ERROR;
 	}